SEC Info  
    Home      Search      My Interests      Help      Sign In      Please Sign In

CASI Pharmaceuticals, Inc. – ‘20-F’ for 12/31/23 – ‘EX-101.DEF’

On:  Thursday, 3/28/24, at 11:01am ET   ·   For:  12/31/23   ·   Accession #:  1558370-24-4190   ·   File #:  1-41666

Previous ‘20-F’:  ‘20-F’ on 4/26/23 for 12/31/22   ·   Latest ‘20-F’:  This Filing   ·   14 References:   

Find Words in Filings emoji
 
  in    Show  and   Hints

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 3/28/24  CASI Pharmaceuticals, Inc.        20-F       12/31/23  142:21M                                    Toppan Merrill Bridge/FA

Annual or Annual-Transition Report by a Foreign Non-Canadian Issuer   —   Form 20-F   —   SEA’34

Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 20-F        Annual or Annual-Transition Report by a Foreign     HTML   3.52M 
                Non-Canadian Issuer                                              
 2: EX-1.1      Underwriting Agreement or Conflict Minerals Report  HTML   1.36M 
 3: EX-2.1      Plan of Acquisition, Reorganization, Arrangement,   HTML     58K 
                Liquidation or Succession                                        
 4: EX-4.29     Instrument Defining the Rights of Security Holders  HTML    230K 
 5: EX-4.37     Instrument Defining the Rights of Security Holders  HTML   1.10M 
 6: EX-4.38     Instrument Defining the Rights of Security Holders  HTML    321K 
 7: EX-4.39     Instrument Defining the Rights of Security Holders  HTML     56K 
 8: EX-4.40     Instrument Defining the Rights of Security Holders  HTML    336K 
 9: EX-4.41     Instrument Defining the Rights of Security Holders  HTML    315K 
10: EX-4.42     Instrument Defining the Rights of Security Holders  HTML    140K 
11: EX-4.43     Instrument Defining the Rights of Security Holders  HTML    128K 
12: EX-4.44     Instrument Defining the Rights of Security Holders  HTML    121K 
13: EX-4.45     Instrument Defining the Rights of Security Holders  HTML    314K 
14: EX-4.46     Instrument Defining the Rights of Security Holders  HTML     92K 
15: EX-4.47     Instrument Defining the Rights of Security Holders  HTML    122K 
16: EX-4.48     Instrument Defining the Rights of Security Holders  HTML     60K 
17: EX-8.1      Opinion of Counsel re: Tax Matters                  HTML     38K 
21: EX-13.1     Annual or Quarterly Report to Security Holders      HTML     41K 
22: EX-13.2     Annual or Quarterly Report to Security Holders      HTML     41K 
24: EX-97.1     Clawback Policy re: Recovery of Erroneously         HTML     62K 
                Awarded Compensation                                             
18: EX-11.1     Statement re: the Computation of Earnings Per       HTML     67K 
                Share                                                            
19: EX-12.1     Statement re: the Computation of Ratios             HTML     44K 
20: EX-12.2     Statement re: the Computation of Ratios             HTML     44K 
23: EX-15.1     Letter re: Unaudited Interim Financial Info         HTML     38K 
30: R1          Document and Entity Information                     HTML    115K 
31: R2          Consolidated Balance Sheets                         HTML    147K 
32: R3          Consolidated Balance Sheets (Parenthetical)         HTML     50K 
33: R4          Consolidated Statements of Operations and           HTML    185K 
                Comprehensive Loss                                               
34: R5          Consolidated Statements of Stockholders' Equity     HTML     90K 
35: R6          Consolidated Statements of Cash Flows               HTML    188K 
36: R7          Description of Business                             HTML     87K 
37: R8          Summary of Significant Accounting Policies          HTML     96K 
38: R9          Investment in Equity Securities, at Fair Value and  HTML    187K 
                Long-Term Investments                                            
39: R10         Inventories                                         HTML     41K 
40: R11         Leases                                              HTML     89K 
41: R12         Property, Plant and Equipment                       HTML     61K 
42: R13         Intangible Assets                                   HTML    111K 
43: R14         Accrued and Other Current Liabilities, and Other    HTML     76K 
                Liabilities                                                      
44: R15         Short Term Borrowings                               HTML     43K 
45: R16         Notes Payable                                       HTML     45K 
46: R17         Grants                                              HTML     42K 
47: R18         Redeemable Noncontrolling Interest and Long Term    HTML     68K 
                Borrowing                                                        
48: R19         Shareholders' Equity                                HTML     66K 
49: R20         Costs of Revenues                                   HTML     40K 
50: R21         Net Loss Per Share                                  HTML     65K 
51: R22         Employee Benefit Plan                               HTML     42K 
52: R23         Share-Based Compensation                            HTML    182K 
53: R24         Income Taxes                                        HTML    159K 
54: R25         Fair Value Measurements                             HTML    118K 
55: R26         Related Party Transactions                          HTML     48K 
56: R27         Commitments and Contingencies                       HTML     44K 
57: R28         Restricted Net Assets                               HTML     41K 
58: R29         Subsequent Events                                   HTML     41K 
59: R30         Condensed Financial Information of Registrant       HTML    220K 
60: R31         Summary of Significant Accounting Policies          HTML    164K 
                (Policies)                                                       
61: R32         Summary of Significant Accounting Policies          HTML     50K 
                (Tables)                                                         
62: R33         Investment in Equity Securities, at Fair Value and  HTML    170K 
                Long-Term Investments (Tables)                                   
63: R34         Leases (Tables)                                     HTML     88K 
64: R35         Property, Plant and Equipment (Tables)              HTML     57K 
65: R36         Intangible Assets (Tables)                          HTML    111K 
66: R37         Accrued and Other Current Liabilities, and Other    HTML     76K 
                Liabilities (Tables)                                             
67: R38         Redeemable Noncontrolling Interest (Tables)         HTML     61K 
68: R39         Shareholders' Equity (Tables)                       HTML     53K 
69: R40         Net Loss Per Share (Tables)                         HTML     64K 
70: R41         Share-Based Compensation (Tables)                   HTML    180K 
71: R42         Income Taxes (Tables)                               HTML    159K 
72: R43         Fair Value Measurements (Tables)                    HTML    117K 
73: R44         Condensed Financial Information of Registrant       HTML    222K 
                (Tables)                                                         
74: R45         DESCRIPTION OF BUSINESS - Liquidity and Capital     HTML    111K 
                Resources (Details)                                              
75: R46         DESCRIPTION OF BUSINESS - License and Distribution  HTML     51K 
                Agreements (China Resources Pharmaceutical                       
                Commercial Group International Trading Co., Ltd.)                
                (Details)                                                        
76: R47         DESCRIPTION OF BUSINESS - License and Distribution  HTML     50K 
                Agreements (Precision Autoimmune Therapeutics Co.,               
                Ltd) (Details)                                                   
77: R48         DESCRIPTION OF BUSINESS - License and Distribution  HTML     47K 
                Agreements (Juventas Cell Therapy Ltd.) (Details)                
78: R49         DESCRIPTION OF BUSINESS - License and Distribution  HTML     72K 
                Agreements (BioInvent International AB) (Details)                
79: R50         DESCRIPTION OF BUSINESS - License and Distribution  HTML     54K 
                Agreements (Black Belt Therapeutics Limited)                     
                (Details)                                                        
80: R51         DESCRIPTION OF BUSINESS - License and Distribution  HTML     56K 
                Agreements (Cleave Therapeutics, Inc.) (Details)                 
81: R52         DESCRIPTION OF BUSINESS - License and Distribution  HTML     48K 
                Agreements (Pharmathen Global BV) (Details)                      
82: R53         SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -        HTML     41K 
                Consolidation (Details)                                          
83: R54         SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -        HTML     40K 
                Segment Reporting (Details)                                      
84: R55         SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash   HTML     47K 
                and Cash Equivalents (Details)                                   
85: R56         SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -        HTML     46K 
                Aggregate Cost And Fair Value (Details)                          
86: R57         Summary of Significant Accounting Policies - Ppe    HTML     48K 
                (Details)                                                        
87: R58         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     66K 
                LONG-TERM INVESTMENTS - Investment in equity                     
                securities, at fair value-MaxCyte Inc. (Details)                 
88: R59         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     94K 
                LONG-TERM INVESTMENTS - Investment in equity                     
                securities, at fair value-BioInvent International                
                AB ordinary shares and warrants (Details)                        
89: R60         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     71K 
                LONG-TERM INVESTMENTS - BioInvent International AB               
                - Summary of Investments (Details)                               
90: R61         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     66K 
                LONG-TERM INVESTMENTS - Summary of Long-term                     
                investments (Details)                                            
91: R62         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     86K 
                LONG-TERM INVESTMENTS - Investment in equity                     
                securities, at fair value-Juventas Cell Therapy                  
                Ltd. (Details)                                                   
92: R63         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     89K 
                LONG-TERM INVESTMENTS - Investment in equity                     
                securities, at fair value-Alesta Therapeutics B.V.               
                (Details)                                                        
93: R64         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     78K 
                LONG-TERM INVESTMENTS - Investment in equity                     
                securities, at fair value-Cleave Therapeutics,                   
                Inc. (Details)                                                   
94: R65         INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND  HTML     75K 
                LONG-TERM INVESTMENTS - Investment in Precision                  
                Autoimmune Therapeutics Co Ltd (Pat) (Details)                   
95: R66         Inventories (Details)                               HTML     43K 
96: R67         Leases - (Details)                                  HTML     57K 
97: R68         Leases - Right of Use Assets and Liabilities        HTML     51K 
                (Details)                                                        
98: R69         LEASES - Supplemental Cash Flow (Details)           HTML     45K 
99: R70         LEASES - Future Undiscounted Cash Flows (Details)   HTML     61K 
100: R71         PROPERTY, PLANT AND EQUIPMENT - Narratives          HTML     50K  
                (Details)                                                        
101: R72         PROPERTY, PLANT AND EQUIPMENT - By type (Details)   HTML     55K  
102: R73         INTANGIBLE ASSETS - Narratives (Details)            HTML     72K  
103: R74         INTANGIBLE ASSETS - Net Definite-lived Intangible   HTML     59K  
                Assets (Details)                                                 
104: R75         INTANGIBLE ASSETS - Intangible Assets Rollforward   HTML     50K  
                (Details)                                                        
105: R76         INTANGIBLE ASSETS - Expected Future Amortization    HTML     52K  
                Expense (Details)                                                
106: R77         Accrued and Other Current Liabilities, and Other    HTML     73K  
                Liabilities (Details)                                            
107: R78         Short Term Borrowings (Details)                     HTML     63K  
108: R79         Notes Payable (Details)                             HTML     50K  
109: R80         Grants (Details)                                    HTML     51K  
110: R81         Redeemable Noncontrolling Interest and Long Term    HTML     96K  
                Borrowing (Details)                                              
111: R82         Redeemable Noncontrolling Interest and Long Term    HTML     51K  
                Borrowing - Changes in Redeemable Noncontrolling                 
                Interest (Details)                                               
112: R83         Shareholders' Equity (Details)                      HTML     83K  
113: R84         Shareholders' Equity - Warrants Activity (Details)  HTML     52K  
114: R85         Costs of Revenues (Details)                         HTML     42K  
115: R86         Net Loss Per Share (Details)                        HTML     43K  
116: R87         Net Loss Per Share - Basic and diluted net loss     HTML     70K  
                per share computation (Details)                                  
117: R88         Employee Benefit Plan (Details)                     HTML     44K  
118: R89         SHARE-BASED COMPENSATION - Compensation Expense     HTML     55K  
                (Details)                                                        
119: R90         SHARE-BASED COMPENSATION - Weighted-Average         HTML     55K  
                Assumptions (Details)                                            
120: R91         SHARE-BASED COMPENSATION - Options Outstanding      HTML     95K  
                (Details)                                                        
121: R92         SHARE-BASED COMPENSATION - Stock Option             HTML     70K  
                Outstanding (Details)                                            
122: R93         Share-Based Compensation (Details)                  HTML     86K  
123: R94         INCOME TAXES - Loss Before Income Taxes (Details)   HTML     50K  
124: R95         INCOME TAXES - Deferred Income Tax Assets And       HTML     72K  
                Liabilities (Details)                                            
125: R96         INCOME TAXES - Reconciliation Of The Provision For  HTML     65K  
                Income Taxes (Details)                                           
126: R97         INCOME TAXES - Valuation allowance (Details)        HTML     47K  
127: R98         INCOME TAXES - Gross Unrecognized Tax Benefits      HTML     45K  
                (Details)                                                        
128: R99         Income Taxes (Details)                              HTML     77K  
129: R100        FAIR VALUE MEASUREMENTS - Financial and             HTML     67K  
                Non-Financial Assets and Liabilities (Details)                   
130: R101        FAIR VALUE MEASUREMENTS - Quantitative Information  HTML     50K  
                about Level 3 Fair Value Measurements (Details)                  
131: R102        Fair Value Measurements (Details)                   HTML     62K  
132: R103        Related Party Transactions (Details)                HTML     83K  
133: R104        Commitments and Contingencies (Details)             HTML     58K  
134: R105        Restricted Net Assets (Details)                     HTML     40K  
135: R106        CONDENSED FINANCIAL INFORMATION OF REGISTRANT -     HTML    150K  
                Condensed Balance Sheets (Details)                               
136: R107        CONDENSED FINANCIAL INFORMATION OF REGISTRANT -     HTML    108K  
                Condensed Statements of Operations and                           
                Comprehensive Loss (Details)                                     
137: R108        CONDENSED FINANCIAL INFORMATION OF REGISTRANT -     HTML    108K  
                Condensed Statements of Cash Flows (Details)                     
139: XML         IDEA XML File -- Filing Summary                      XML    243K  
142: XML         XBRL Instance -- casi-20231231x20f_htm               XML   3.57M  
138: EXCEL       IDEA Workbook of Financial Report Info              XLSX    249K  
26: EX-101.CAL  XBRL Calculations -- casi-20231231_cal               XML    267K 
27: EX-101.DEF  XBRL Definitions -- casi-20231231_def                XML   1.32M 
28: EX-101.LAB  XBRL Labels -- casi-20231231_lab                     XML   1.83M 
29: EX-101.PRE  XBRL Presentations -- casi-20231231_pre              XML   1.74M 
25: EX-101.SCH  XBRL Schema -- casi-20231231                         XSD    324K 
140: JSON        XBRL Instance as JSON Data -- MetaLinks              668±  1.06M  
141: ZIP         XBRL Zipped Folder -- 0001558370-24-004190-xbrl      Zip   1.32M  


‘EX-101.DEF’   —   XBRL Definitions — casi-20231231_def


This Exhibit is an XBRL File.


                                                                                                                                                                                
<?xml version="1.0" encoding="windows-1252"?>
<!-- XBRL document created with Toppan Merrill Bridge 10.5.0.8 -->
<!-- Based on XBRL 2.1 -->
<!-- Created on: 3/28/2024 2:06:03 PM -->
<!-- Modified on: 3/28/2024 2:06:03 PM -->
<link:linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrli="http://www.xbrl.org/2003/instance">
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DocumentDocumentAndEntityInformation" roleURI="http://www.entremed.com/role/DocumentDocumentAndEntityInformation"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#StatementConsolidatedStatementsOfStockholdersEquity" roleURI="http://www.entremed.com/role/StatementConsolidatedStatementsOfStockholdersEquity"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#StatementConsolidatedStatementsOfCashFlows" roleURI="http://www.entremed.com/role/StatementConsolidatedStatementsOfCashFlows"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureFairValueMeasurementsTables" roleURI="http://www.entremed.com/role/DisclosureFairValueMeasurementsTables"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLiquidityAndCapitalResourcesDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLiquidityAndCapitalResourcesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCoLtdDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCoLtdDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPrecisionAutoimmuneTherapeuticsCoLtdDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPrecisionAutoimmuneTherapeuticsCoLtdDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsJuventasCellTherapyLtdDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsJuventasCellTherapyLtdDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBioinventInternationalAbDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBioinventInternationalAbDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBlackBeltTherapeuticsLimitedDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBlackBeltTherapeuticsLimitedDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsCleaveTherapeuticsIncDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsCleaveTherapeuticsIncDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPharmathenGlobalBvDetails" roleURI="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPharmathenGlobalBvDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails" roleURI="http://www.entremed.com/role/DisclosureSummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesPpeDetails" roleURI="http://www.entremed.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPpeDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueMaxcyteIncDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueMaxcyteIncDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueBioinventInternationalAbOrdinarySharesAndWarrantsDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueBioinventInternationalAbOrdinarySharesAndWarrantsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsBioinventInternationalAbSummaryOfInvestmentsDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsBioinventInternationalAbSummaryOfInvestmentsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsSummaryOfLongTermInvestmentsDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsSummaryOfLongTermInvestmentsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueJuventasCellTherapyLtdDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueJuventasCellTherapyLtdDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueAlestaTherapeuticsBvDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueAlestaTherapeuticsBvDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueCleaveTherapeuticsIncDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueCleaveTherapeuticsIncDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInPrecisionAutoimmuneTherapeuticsCoLtdPatDetails" roleURI="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInPrecisionAutoimmuneTherapeuticsCoLtdPatDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureLeasesDetails" roleURI="http://www.entremed.com/role/DisclosureLeasesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosurePropertyPlantAndEquipmentNarrativesDetails" roleURI="http://www.entremed.com/role/DisclosurePropertyPlantAndEquipmentNarrativesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureIntangibleAssetsNarrativesDetails" roleURI="http://www.entremed.com/role/DisclosureIntangibleAssetsNarrativesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureIntangibleAssetsNetDefiniteLivedIntangibleAssetsDetails" roleURI="http://www.entremed.com/role/DisclosureIntangibleAssetsNetDefiniteLivedIntangibleAssetsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShortTermBorrowingsDetails" roleURI="http://www.entremed.com/role/DisclosureShortTermBorrowingsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureNotesPayableDetails" roleURI="http://www.entremed.com/role/DisclosureNotesPayableDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureGrantsDetails" roleURI="http://www.entremed.com/role/DisclosureGrantsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureRedeemableNoncontrollingInterestAndLongTermBorrowingDetails" roleURI="http://www.entremed.com/role/DisclosureRedeemableNoncontrollingInterestAndLongTermBorrowingDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShareholdersEquityDetails" roleURI="http://www.entremed.com/role/DisclosureShareholdersEquityDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureCostsOfRevenuesDetails" roleURI="http://www.entremed.com/role/DisclosureCostsOfRevenuesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureNetLossPerShareDetails" roleURI="http://www.entremed.com/role/DisclosureNetLossPerShareDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShareBasedCompensationCompensationExpenseDetails" roleURI="http://www.entremed.com/role/DisclosureShareBasedCompensationCompensationExpenseDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShareBasedCompensationOptionsOutstandingDetails" roleURI="http://www.entremed.com/role/DisclosureShareBasedCompensationOptionsOutstandingDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShareBasedCompensationStockOptionOutstandingDetails" roleURI="http://www.entremed.com/role/DisclosureShareBasedCompensationStockOptionOutstandingDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureShareBasedCompensationDetails" roleURI="http://www.entremed.com/role/DisclosureShareBasedCompensationDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureIncomeTaxesDetails" roleURI="http://www.entremed.com/role/DisclosureIncomeTaxesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureFairValueMeasurementsFinancialAndNonFinancialAssetsAndLiabilitiesDetails" roleURI="http://www.entremed.com/role/DisclosureFairValueMeasurementsFinancialAndNonFinancialAssetsAndLiabilitiesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureFairValueMeasurementsQuantitativeInformationAboutLevel3FairValueMeasurementsDetails" roleURI="http://www.entremed.com/role/DisclosureFairValueMeasurementsQuantitativeInformationAboutLevel3FairValueMeasurementsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureFairValueMeasurementsDetails" roleURI="http://www.entremed.com/role/DisclosureFairValueMeasurementsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureRelatedPartyTransactionsDetails" roleURI="http://www.entremed.com/role/DisclosureRelatedPartyTransactionsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureCommitmentsAndContingenciesDetails" roleURI="http://www.entremed.com/role/DisclosureCommitmentsAndContingenciesDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureCondensedFinancialInformationOfRegistrantCondensedBalanceSheetsDetails" roleURI="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedBalanceSheetsDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfOperationsAndComprehensiveLossDetails" roleURI="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfOperationsAndComprehensiveLossDetails"/>
<link:roleRef xlink:type="simple" xlink:href="casi-20231231.xsd#DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfCashFlowsDetails" roleURI="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfCashFlowsDetails"/>
<link:arcroleRef arcroleURI="http://www.esma.europa.eu/xbrl/esef/arcrole/wider-narrower" xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/arcrole/esma-arcrole-2018-11-21.xsd#wider-narrower"/>
<link:roleRef roleURI="http://www.entremed.com/role/DisclosureStandardAndCustomAxisDomainDefaults" xlink:href="casi-20231231.xsd#DisclosureStandardAndCustomAxisDomainDefaults" xlink:type="simple"/>
<link:roleRef xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-roles-2023.xsd#eedm" roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
<link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended" xlink:title="Extensible Enumeration Domain Members">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" xlink:title="us-gaap_LiabilitiesCurrentAbstract"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent" xlink:title="us-gaap_AccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrent" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_LiabilitiesCurrentAbstract To us-gaap_AccruedLiabilitiesCurrent" order="1" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAbstract" xlink:label="us-gaap_LiabilitiesAbstract" xlink:title="us-gaap_LiabilitiesAbstract"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="us-gaap_OtherLiabilitiesNoncurrent" xlink:title="us-gaap_OtherLiabilitiesNoncurrent"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_OtherLiabilitiesNoncurrent" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_LiabilitiesAbstract To us-gaap_OtherLiabilitiesNoncurrent" order="1" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent_1" xlink:title="us-gaap_AccruedLiabilitiesCurrent_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LiabilitiesAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrent_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_LiabilitiesAbstract To us-gaap_AccruedLiabilitiesCurrent_1" order="2" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract" xlink:title="us-gaap_AssetsAbstract"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_1" xlink:title="us-gaap_OperatingLeaseRightOfUseAsset_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_AssetsAbstract To us-gaap_OperatingLeaseRightOfUseAsset_1" order="1" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" xlink:title="us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_LiabilitiesCurrentAbstract To us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" order="2" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract" xlink:title="us-gaap_LiabilitiesNoncurrentAbstract"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract" xlink:title="us-gaap_IncomeStatementAbstract"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ResearchAndDevelopmentInProcess1" xlink:label="casi_ResearchAndDevelopmentInProcess1" xlink:title="us-gaap_ResearchAndDevelopmentInProcess_2"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="casi_ResearchAndDevelopmentInProcess1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_IncomeStatementAbstract To us-gaap_ResearchAndDevelopmentInProcess_2" order="1" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain" xlink:title="us-gaap_RelatedPartyTransactionDomain"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyMember" xlink:label="us-gaap_RelatedPartyMember" xlink:title="us-gaap_RelatedPartyMember"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_RelatedPartyTransactionDomain" xlink:to="us-gaap_RelatedPartyMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_RelatedPartyTransactionDomain To us-gaap_RelatedPartyMember" order="1" priority="0"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyMember" xlink:label="us-gaap_RelatedPartyMember_2" xlink:title="us-gaap_RelatedPartyMember_2"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain" xlink:title="us-gaap_RelatedPartyDomain"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyMember" xlink:label="us-gaap_RelatedPartyMember_4" xlink:title="us-gaap_RelatedPartyMember_4"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_RelatedPartyMember_4" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_RelatedPartyDomain To us-gaap_RelatedPartyMember_4" order="1" priority="0"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureStandardAndCustomAxisDomainDefaults" xlink:type="extended" xlink:title="99900 - Disclosure - Standard And Custom Axis Domain Defaults">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis_1" xlink:title="srt_ProductOrServiceAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain_1" xlink:title="srt_ProductsAndServicesDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_ProductOrServiceAxis_1" xlink:to="srt_ProductsAndServicesDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_ProductOrServiceAxis_1 To srt_ProductsAndServicesDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis_1" xlink:title="us-gaap_StatementEquityComponentsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_1" xlink:title="us-gaap_EquityComponentDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_StatementEquityComponentsAxis_1" xlink:to="us-gaap_EquityComponentDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_StatementEquityComponentsAxis_1 To us-gaap_EquityComponentDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis_1" xlink:title="srt_CumulativeEffectPeriodOfAdoptionAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain_1" xlink:title="srt_CumulativeEffectPeriodOfAdoptionDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_CumulativeEffectPeriodOfAdoptionAxis_1" xlink:to="srt_CumulativeEffectPeriodOfAdoptionDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_CumulativeEffectPeriodOfAdoptionAxis_1 To srt_CumulativeEffectPeriodOfAdoptionDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis_1" xlink:title="srt_CounterpartyNameAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1" xlink:title="srt_RepurchaseAgreementCounterpartyNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_CounterpartyNameAxis_1" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_CounterpartyNameAxis_1 To srt_RepurchaseAgreementCounterpartyNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_1" xlink:title="us-gaap_FairValueByMeasurementFrequencyAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_1" xlink:title="us-gaap_FairValueMeasurementFrequencyDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis_1" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByMeasurementFrequencyAxis_1 To us-gaap_FairValueMeasurementFrequencyDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis_1" xlink:title="dei_LegalEntityAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_1" xlink:title="dei_EntityDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="dei_LegalEntityAxis_1" xlink:to="dei_EntityDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:dei_LegalEntityAxis_1 To dei_EntityDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis_1" xlink:title="srt_RangeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_1" xlink:title="srt_RangeMember_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_RangeAxis_1" xlink:to="srt_RangeMember_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_RangeAxis_1 To srt_RangeMember_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis_1" xlink:title="srt_ConsolidatedEntitiesAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain_1" xlink:title="srt_ConsolidatedEntitiesDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_ConsolidatedEntitiesAxis_1" xlink:to="srt_ConsolidatedEntitiesDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_ConsolidatedEntitiesAxis_1 To srt_ConsolidatedEntitiesDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsAxis" xlink:label="srt_ConsolidationItemsAxis_1" xlink:title="srt_ConsolidationItemsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain" xlink:label="srt_ConsolidationItemsDomain_1" xlink:title="srt_ConsolidationItemsDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_ConsolidationItemsAxis_1" xlink:to="srt_ConsolidationItemsDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_ConsolidationItemsAxis_1 To srt_ConsolidationItemsDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsContractCounterpartyAxis" xlink:label="casi_InvestmentsContractCounterpartyAxis_1" xlink:title="casi_InvestmentsContractCounterpartyAxis_1"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsContractCounterpartyDomain" xlink:label="casi_InvestmentsContractCounterpartyDomain_1" xlink:title="casi_InvestmentsContractCounterpartyDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="casi_InvestmentsContractCounterpartyAxis_1" xlink:to="casi_InvestmentsContractCounterpartyDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:casi_InvestmentsContractCounterpartyAxis_1 To casi_InvestmentsContractCounterpartyDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_1" xlink:title="us-gaap_FairValueByFairValueHierarchyLevelAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1" xlink:title="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis_1" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByFairValueHierarchyLevelAxis_1 To us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeAxis_1" xlink:title="us-gaap_OptionIndexedToIssuersEquityTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeDomain_1" xlink:title="us-gaap_OptionIndexedToIssuersEquityTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeAxis_1" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_OptionIndexedToIssuersEquityTypeAxis_1 To us-gaap_OptionIndexedToIssuersEquityTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis_1" xlink:title="us-gaap_MeasurementInputTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain_1" xlink:title="us-gaap_MeasurementInputTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_MeasurementInputTypeAxis_1" xlink:to="us-gaap_MeasurementInputTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_MeasurementInputTypeAxis_1 To us-gaap_MeasurementInputTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis_1" xlink:title="us-gaap_DebtInstrumentAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_1" xlink:title="us-gaap_DebtInstrumentNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_DebtInstrumentAxis_1" xlink:to="us-gaap_DebtInstrumentNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_DebtInstrumentAxis_1 To us-gaap_DebtInstrumentNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis_1" xlink:title="us-gaap_SubsequentEventTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_1" xlink:title="us-gaap_SubsequentEventTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_SubsequentEventTypeAxis_1" xlink:to="us-gaap_SubsequentEventTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_SubsequentEventTypeAxis_1 To us-gaap_SubsequentEventTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis_1" xlink:title="us-gaap_FinancialInstrumentAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" xlink:title="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_FinancialInstrumentAxis_1" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FinancialInstrumentAxis_1 To us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_1" xlink:title="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember_1" xlink:title="us-gaap_TypeOfAdoptionMember_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_1" xlink:to="us-gaap_TypeOfAdoptionMember_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_1 To us-gaap_TypeOfAdoptionMember_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis_1" xlink:title="srt_StatementGeographicalAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain_1" xlink:title="srt_SegmentGeographicalDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_StatementGeographicalAxis_1" xlink:to="srt_SegmentGeographicalDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_StatementGeographicalAxis_1 To srt_SegmentGeographicalDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LeaseContractualTermAxis" xlink:label="us-gaap_LeaseContractualTermAxis_1" xlink:title="us-gaap_LeaseContractualTermAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LeaseContractualTermDomain" xlink:label="us-gaap_LeaseContractualTermDomain_1" xlink:title="us-gaap_LeaseContractualTermDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LeaseContractualTermAxis_1" xlink:to="us-gaap_LeaseContractualTermDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_LeaseContractualTermAxis_1 To us-gaap_LeaseContractualTermDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis_1" xlink:title="us-gaap_BalanceSheetLocationAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain_1" xlink:title="us-gaap_BalanceSheetLocationDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_BalanceSheetLocationAxis_1" xlink:to="us-gaap_BalanceSheetLocationDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_BalanceSheetLocationAxis_1 To us-gaap_BalanceSheetLocationDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis_1" xlink:title="us-gaap_TypeOfArrangementAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_1" xlink:title="us-gaap_ArrangementsAndNonarrangementTransactionsMember_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_TypeOfArrangementAxis_1" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_TypeOfArrangementAxis_1 To us-gaap_ArrangementsAndNonarrangementTransactionsMember_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:title="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" xlink:title="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1 To us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis_1" xlink:title="us-gaap_LineOfCreditFacilityAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_1" xlink:title="us-gaap_LineOfCreditFacilityLenderDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LineOfCreditFacilityAxis_1" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_LineOfCreditFacilityAxis_1 To us-gaap_LineOfCreditFacilityLenderDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1" xlink:title="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_1" xlink:title="us-gaap_RelatedPartyDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1" xlink:to="us-gaap_RelatedPartyDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_1 To us-gaap_RelatedPartyDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis_1" xlink:title="us-gaap_BusinessAcquisitionAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_1" xlink:title="us-gaap_BusinessAcquisitionAcquireeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_BusinessAcquisitionAxis_1" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_BusinessAcquisitionAxis_1 To us-gaap_BusinessAcquisitionAcquireeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_1" xlink:title="us-gaap_StatementClassOfStockAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_1" xlink:title="us-gaap_ClassOfStockDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_StatementClassOfStockAxis_1" xlink:to="us-gaap_ClassOfStockDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_StatementClassOfStockAxis_1 To us-gaap_ClassOfStockDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_1" xlink:title="us-gaap_SubsidiarySaleOfStockAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_1" xlink:title="us-gaap_SaleOfStockNameOfTransactionDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_1" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_SubsidiarySaleOfStockAxis_1 To us-gaap_SaleOfStockNameOfTransactionDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis_1" xlink:title="srt_TitleOfIndividualAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_1" xlink:title="srt_TitleOfIndividualWithRelationshipToEntityDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_TitleOfIndividualAxis_1" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_TitleOfIndividualAxis_1 To srt_TitleOfIndividualWithRelationshipToEntityDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis_1" xlink:title="us-gaap_IncomeStatementLocationAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_1" xlink:title="us-gaap_IncomeStatementLocationDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_IncomeStatementLocationAxis_1" xlink:to="us-gaap_IncomeStatementLocationDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_IncomeStatementLocationAxis_1 To us-gaap_IncomeStatementLocationDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis" xlink:label="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis_1" xlink:title="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain" xlink:label="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_1" xlink:title="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis_1" xlink:to="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis_1 To us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis_1" xlink:title="us-gaap_AwardTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" xlink:title="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_AwardTypeAxis_1" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_AwardTypeAxis_1 To us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis_1" xlink:title="us-gaap_PlanNameAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain_1" xlink:title="us-gaap_PlanNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_PlanNameAxis_1" xlink:to="us-gaap_PlanNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_PlanNameAxis_1 To us-gaap_PlanNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="us-gaap_TaxCreditCarryforwardAxis_1" xlink:title="us-gaap_TaxCreditCarryforwardAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_1" xlink:title="us-gaap_TaxCreditCarryforwardNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_TaxCreditCarryforwardAxis_1" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_TaxCreditCarryforwardAxis_1 To us-gaap_TaxCreditCarryforwardNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="us-gaap_IncomeTaxAuthorityAxis_1" xlink:title="us-gaap_IncomeTaxAuthorityAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain_1" xlink:title="us-gaap_IncomeTaxAuthorityDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_IncomeTaxAuthorityAxis_1" xlink:to="us-gaap_IncomeTaxAuthorityDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_IncomeTaxAuthorityAxis_1 To us-gaap_IncomeTaxAuthorityDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis_1" xlink:title="us-gaap_PropertyPlantAndEquipmentByTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_1" xlink:title="us-gaap_PropertyPlantAndEquipmentTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis_1" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_PropertyPlantAndEquipmentByTypeAxis_1 To us-gaap_PropertyPlantAndEquipmentTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis_1" xlink:title="srt_StatementScenarioAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain_1" xlink:title="srt_ScenarioUnspecifiedDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_StatementScenarioAxis_1" xlink:to="srt_ScenarioUnspecifiedDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_StatementScenarioAxis_1 To srt_ScenarioUnspecifiedDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis_1" xlink:title="us-gaap_StatementBusinessSegmentsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain_1" xlink:title="us-gaap_SegmentDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_StatementBusinessSegmentsAxis_1" xlink:to="us-gaap_SegmentDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_StatementBusinessSegmentsAxis_1 To us-gaap_SegmentDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:title="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" xlink:title="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_1 To us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis" xlink:label="us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_1" xlink:title="us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongLivedAssetsHeldForSaleNameDomain" xlink:label="us-gaap_LongLivedAssetsHeldForSaleNameDomain_1" xlink:title="us-gaap_LongLivedAssetsHeldForSaleNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_1" xlink:to="us-gaap_LongLivedAssetsHeldForSaleNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis_1 To us-gaap_LongLivedAssetsHeldForSaleNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="us-gaap_FairValueByAssetClassAxis_1" xlink:title="us-gaap_FairValueByAssetClassAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1" xlink:title="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByAssetClassAxis_1" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByAssetClassAxis_1 To us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="us-gaap_ValuationTechniqueAxis_1" xlink:title="us-gaap_ValuationTechniqueAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain_1" xlink:title="us-gaap_ValuationTechniqueDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_ValuationTechniqueAxis_1" xlink:to="us-gaap_ValuationTechniqueDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_ValuationTechniqueAxis_1 To us-gaap_ValuationTechniqueDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ConstructionAgreementsAxis" xlink:label="casi_ConstructionAgreementsAxis_1" xlink:title="casi_ConstructionAgreementsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ConstructionAgreementsDomain" xlink:label="casi_ConstructionAgreementsDomain_1" xlink:title="casi_ConstructionAgreementsDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="casi_ConstructionAgreementsAxis_1" xlink:to="casi_ConstructionAgreementsDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:casi_ConstructionAgreementsAxis_1 To casi_ConstructionAgreementsDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:title="us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain" xlink:title="us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_1 To us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis_1" xlink:title="us-gaap_InvestmentTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember_1" xlink:title="us-gaap_InvestmentTypeCategorizationMember_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_InvestmentTypeAxis_1" xlink:to="us-gaap_InvestmentTypeCategorizationMember_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_InvestmentTypeAxis_1 To us-gaap_InvestmentTypeCategorizationMember_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_1" xlink:title="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_1" xlink:title="srt_EquityMethodInvesteeNameDomain_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressesAddressTypeAxis" xlink:label="dei_EntityAddressesAddressTypeAxis_1" xlink:title="dei_EntityAddressesAddressTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AddressTypeDomain" xlink:label="dei_AddressTypeDomain_1" xlink:title="dei_AddressTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="dei_EntityAddressesAddressTypeAxis_1" xlink:to="dei_AddressTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:dei_EntityAddressesAddressTypeAxis_1 To dei_AddressTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1" xlink:title="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_1" xlink:title="us-gaap_AntidilutiveSecuritiesNameDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_1 To us-gaap_AntidilutiveSecuritiesNameDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RestatementAxis" xlink:label="srt_RestatementAxis_1" xlink:title="srt_RestatementAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RestatementDomain" xlink:label="srt_RestatementDomain_1" xlink:title="srt_RestatementDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_RestatementAxis_1" xlink:to="srt_RestatementDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_RestatementAxis_1 To srt_RestatementDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1" xlink:title="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1" xlink:title="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1 To us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PublicUtilitiesInventoryAxis" xlink:label="us-gaap_PublicUtilitiesInventoryAxis_1" xlink:title="us-gaap_PublicUtilitiesInventoryAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain" xlink:label="us-gaap_PublicUtilitiesInventoryTypeDomain_1" xlink:title="us-gaap_PublicUtilitiesInventoryTypeDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_PublicUtilitiesInventoryAxis_1" xlink:to="us-gaap_PublicUtilitiesInventoryTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_PublicUtilitiesInventoryAxis_1 To us-gaap_PublicUtilitiesInventoryTypeDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="us-gaap_RelatedPartyTransactionAxis_1" xlink:title="us-gaap_RelatedPartyTransactionAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain_2" xlink:title="us-gaap_RelatedPartyTransactionDomain_2"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_RelatedPartyTransactionAxis_1" xlink:to="us-gaap_RelatedPartyTransactionDomain_2" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_RelatedPartyTransactionAxis_1 To us-gaap_RelatedPartyTransactionDomain_2" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_OwnershipAxis" xlink:label="srt_OwnershipAxis_1" xlink:title="srt_OwnershipAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_OwnershipDomain" xlink:label="srt_OwnershipDomain_1" xlink:title="srt_OwnershipDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="srt_OwnershipAxis_1" xlink:to="srt_OwnershipDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_OwnershipAxis_1 To srt_OwnershipDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedAndNonrelatedPartyStatusAxis" xlink:label="us-gaap_RelatedAndNonrelatedPartyStatusAxis_1" xlink:title="us-gaap_RelatedAndNonrelatedPartyStatusAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedAndNonrelatedPartyStatusDomain" xlink:label="us-gaap_RelatedAndNonrelatedPartyStatusDomain_1" xlink:title="us-gaap_RelatedAndNonrelatedPartyStatusDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_RelatedAndNonrelatedPartyStatusAxis_1" xlink:to="us-gaap_RelatedAndNonrelatedPartyStatusDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_RelatedAndNonrelatedPartyStatusAxis_1 To us-gaap_RelatedAndNonrelatedPartyStatusDomain_1" order="1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsAxis" xlink:label="us-gaap_DividendsAxis_1" xlink:title="us-gaap_DividendsAxis_1"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsDomain" xlink:label="us-gaap_DividendsDomain_1" xlink:title="us-gaap_DividendsDomain_1"/>
<link:definitionArc xlink:type="arc" xlink:from="us-gaap_DividendsAxis_1" xlink:to="us-gaap_DividendsDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_DividendsAxis_1 To us-gaap_DividendsDomain_1" order="1"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DocumentDocumentAndEntityInformation" xlink:type="extended" xlink:title="00090 - Document - Document and Entity Information">
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationTable" xlink:label="dei_DocumentInformationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressesAddressTypeAxis" xlink:label="dei_EntityAddressesAddressTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="dei_DocumentInformationTable" xlink:to="dei_EntityAddressesAddressTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AddressTypeDomain" xlink:label="dei_AddressTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_EntityAddressesAddressTypeAxis" xlink:to="dei_AddressTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AddressTypeDomain" xlink:label="dei_AddressTypeDomain_638472315573122003"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_EntityAddressesAddressTypeAxis" xlink:to="dei_AddressTypeDomain_638472315573122003" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_BusinessContactMember" xlink:label="dei_BusinessContactMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_AddressTypeDomain" xlink:to="dei_BusinessContactMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationLineItems" xlink:label="dei_DocumentInformationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentInformationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentType" xlink:label="dei_DocumentType"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentType" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentRegistrationStatement" xlink:label="dei_DocumentRegistrationStatement"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentRegistrationStatement" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentAnnualReport" xlink:label="dei_DocumentAnnualReport"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentAnnualReport" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentPeriodEndDate" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_CurrentFiscalYearEndDate" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalYearFocus" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentTransitionReport" xlink:label="dei_DocumentTransitionReport"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentTransitionReport" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentShellCompanyReport" xlink:label="dei_DocumentShellCompanyReport"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentShellCompanyReport" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFileNumber" xlink:label="dei_EntityFileNumber"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityFileNumber" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityRegistrantName" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="dei_EntityIncorporationStateCountryCode"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityIncorporationStateCountryCode" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_ContactPersonnelName" xlink:label="dei_ContactPersonnelName"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_ContactPersonnelName" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressAddressLine1" xlink:label="dei_EntityAddressAddressLine1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressAddressLine1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressAddressLine2" xlink:label="dei_EntityAddressAddressLine2"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressAddressLine2" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressCityOrTown" xlink:label="dei_EntityAddressCityOrTown"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressCityOrTown" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressPostalZipCode" xlink:label="dei_EntityAddressPostalZipCode"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressPostalZipCode" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressStateOrProvince" xlink:label="dei_EntityAddressStateOrProvince"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressStateOrProvince" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressCountry" xlink:label="dei_EntityAddressCountry"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityAddressCountry" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CityAreaCode" xlink:label="dei_CityAreaCode"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_CityAreaCode" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LocalPhoneNumber" xlink:label="dei_LocalPhoneNumber"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_LocalPhoneNumber" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_ContactPersonnelEmailAddress" xlink:label="dei_ContactPersonnelEmailAddress"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="22" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_ContactPersonnelEmailAddress" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_Security12bTitle" xlink:label="dei_Security12bTitle"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="23" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_Security12bTitle" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_TradingSymbol" xlink:label="dei_TradingSymbol"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="24" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_TradingSymbol" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_SecurityExchangeName" xlink:label="dei_SecurityExchangeName"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="25" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_SecurityExchangeName" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="26" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCommonStockSharesOutstanding" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityWellKnownSeasonedIssuer" xlink:label="dei_EntityWellKnownSeasonedIssuer"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="27" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityWellKnownSeasonedIssuer" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityVoluntaryFilers" xlink:label="dei_EntityVoluntaryFilers"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="28" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityVoluntaryFilers" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="29" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCurrentReportingStatus" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityInteractiveDataCurrent" xlink:label="dei_EntityInteractiveDataCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="30" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityInteractiveDataCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="31" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityFilerCategory" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityEmergingGrowthCompany" xlink:label="dei_EntityEmergingGrowthCompany"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="32" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityEmergingGrowthCompany" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_IcfrAuditorAttestationFlag" xlink:label="dei_IcfrAuditorAttestationFlag"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="33" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_IcfrAuditorAttestationFlag" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFinStmtErrorCorrectionFlag" xlink:label="dei_DocumentFinStmtErrorCorrectionFlag"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="34" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFinStmtErrorCorrectionFlag" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentAccountingStandard" xlink:label="dei_DocumentAccountingStandard"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="35" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentAccountingStandard" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityShellCompany" xlink:label="dei_EntityShellCompany"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="36" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityShellCompany" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AuditorFirmId" xlink:label="dei_AuditorFirmId"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="37" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AuditorFirmId" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AuditorName" xlink:label="dei_AuditorName"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="38" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AuditorName" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AuditorLocation" xlink:label="dei_AuditorLocation"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="39" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AuditorLocation" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="40" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_EntityCentralIndexKey" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="41" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentFiscalPeriodFocus" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="42" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_AmendmentFlag" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/StatementConsolidatedStatementsOfStockholdersEquity" xlink:type="extended" xlink:title="00300 - Statement - Consolidated Statements of Stockholders' Equity">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_638472315573222000"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_638472315573222000" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonMember" xlink:label="us-gaap_TreasuryStockCommonMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockCommonMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesOutstanding" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_StockIssuedDuringPeriodValueCommonStockPursuantToFinancingAgreements" xlink:label="casi_StockIssuedDuringPeriodValueCommonStockPursuantToFinancingAgreements"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_StockIssuedDuringPeriodValueCommonStockPursuantToFinancingAgreements" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_StockIssuedDuringPeriodSharesCommonStockPursuantToFinancingAgreements" xlink:label="casi_StockIssuedDuringPeriodSharesCommonStockPursuantToFinancingAgreements"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="casi_StockIssuedDuringPeriodValueCommonStockPursuantToFinancingAgreements" xlink:to="casi_StockIssuedDuringPeriodSharesCommonStockPursuantToFinancingAgreements" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax" xlink:label="us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/StatementConsolidatedStatementsOfCashFlows" xlink:type="extended" xlink:title="00400 - Statement - Consolidated Statements of Cash Flows">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_638472315573262004"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_638472315573262004" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" xlink:label="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573262004"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573262004" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BlackBeltTxLimitedMember" xlink:label="casi_BlackBeltTxLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BlackBeltTxLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AlestaTxMember" xlink:label="casi_AlestaTxMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AlestaTxMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProfitLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DepreciationAndAmortization" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AmortizationOfIntangibleAssetsAndHeldForSale" xlink:label="casi_AmortizationOfIntangibleAssetsAndHeldForSale"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="casi_AmortizationOfIntangibleAssetsAndHeldForSale" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ReductionInCarryingAmountOfRightOfUseAssets" xlink:label="casi_ReductionInCarryingAmountOfRightOfUseAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="casi_ReductionInCarryingAmountOfRightOfUseAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnDispositionOfIntangibleAssets" xlink:label="us-gaap_GainLossOnDispositionOfIntangibleAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnDispositionOfIntangibleAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ImpairmentOfIntangibleAssetsFinitelived" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ResearchAndDevelopmentInProcessAcquired" xlink:label="casi_ResearchAndDevelopmentInProcessAcquired"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="casi_ResearchAndDevelopmentInProcessAcquired" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_GovernmentGrant" xlink:label="casi_GovernmentGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="casi_GovernmentGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncomeLossFromEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesRealizedGainLoss" xlink:label="us-gaap_DebtSecuritiesRealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DebtSecuritiesRealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal" xlink:label="us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ImpairmentLossOfLongTermInvestments" xlink:label="casi_ImpairmentLossOfLongTermInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="casi_ImpairmentLossOfLongTermInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInDueFromRelatedPartiesCurrent" xlink:label="us-gaap_IncreaseDecreaseInDueFromRelatedPartiesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInDueFromRelatedPartiesCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInInventories" xlink:label="us-gaap_IncreaseDecreaseInInventories"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInInventories" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsPayableTrade" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableTrade"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableTrade" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" xlink:label="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi" xlink:label="us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromSaleOfEquityMethodInvestments" xlink:label="us-gaap_ProceedsFromSaleOfEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PurchaseOfShortTermInvestmentsAndTermDeposits" xlink:label="casi_PurchaseOfShortTermInvestmentsAndTermDeposits"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_PurchaseOfShortTermInvestmentsAndTermDeposits" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromSalesOrMaturityOfShortTermInvestmentsAndTermDeposits" xlink:label="casi_ProceedsFromSalesOrMaturityOfShortTermInvestmentsAndTermDeposits"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ProceedsFromSalesOrMaturityOfShortTermInvestmentsAndTermDeposits" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromGovernmentGrant" xlink:label="casi_ProceedsFromGovernmentGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ProceedsFromGovernmentGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireIntangibleAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan" xlink:label="casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment" xlink:label="us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="us-gaap_PaymentsToAcquireInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ReceiptOfRepaymentOfConvertibleNote" xlink:label="casi_ReceiptOfRepaymentOfConvertibleNote"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ReceiptOfRepaymentOfConvertibleNote" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ReceiptOfGovernmentGrant" xlink:label="casi_ReceiptOfGovernmentGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ReceiptOfGovernmentGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromLinesOfCredit" xlink:label="us-gaap_ProceedsFromLinesOfCredit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromLinesOfCredit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfNotesPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfDividendsMinorityInterest" xlink:label="us-gaap_PaymentsOfDividendsMinorityInterest"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDividendsMinorityInterest" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromIssuanceOfCommonStockAndWarrants" xlink:label="casi_ProceedsFromIssuanceOfCommonStockAndWarrants"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="casi_ProceedsFromIssuanceOfCommonStockAndWarrants" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockOptionsExercised" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestPaidNet" xlink:label="us-gaap_InterestPaidNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_InterestPaidNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="us-gaap_IncomeTaxesPaidNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_IncomeTaxesPaidNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:label="us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoncashInvestingAndFinancingItemsAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="us-gaap_CapitalExpendituresIncurredButNotYetPaid" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="us-gaap_DebtConversionConvertedInstrumentAmount1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NonCashInvestingLoanForgiveness" xlink:label="casi_NonCashInvestingLoanForgiveness"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="casi_NonCashInvestingLoanForgiveness" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureFairValueMeasurementsTables" xlink:type="extended" xlink:title="31903 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_638472315573442008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_638472315573442008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLiquidityAndCapitalResourcesDetails" xlink:type="extended" xlink:title="40101 - Disclosure - DESCRIPTION OF BUSINESS - Liquidity and Capital Resources (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315573452012"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315573452012" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CASIWuxiMember" xlink:label="casi_CASIWuxiMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CASIWuxiMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_WuxiLpMember" xlink:label="casi_WuxiLpMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="dei_EntityDomain" xlink:to="casi_WuxiLpMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CasiChinaMember" xlink:label="casi_CasiChinaMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="dei_EntityDomain" xlink:to="casi_CasiChinaMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315573462010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315573462010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FolotynMember" xlink:label="casi_FolotynMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_FolotynMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_TypeOfArrangementAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573462010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573462010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember" xlink:label="casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SupplyAgreementWithAcrotechInc.Member" xlink:label="casi_SupplyAgreementWithAcrotechInc.Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_SupplyAgreementWithAcrotechInc.Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_638472315573472008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain_638472315573472008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ConvertibleLoanMember" xlink:label="casi_ConvertibleLoanMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="casi_ConvertibleLoanMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315573482008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315573482008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OperatingLeaseRightOfUseReturned" xlink:label="casi_OperatingLeaseRightOfUseReturned"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_OperatingLeaseRightOfUseReturned" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnDispositionOfAssets1" xlink:label="us-gaap_GainLossOnDispositionOfAssets1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_GainLossOnDispositionOfAssets1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromGovernmentGrant" xlink:label="casi_ProceedsFromGovernmentGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ProceedsFromGovernmentGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfGuaranteeAgreements" xlink:label="casi_NumberOfGuaranteeAgreements"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_NumberOfGuaranteeAgreements" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentPrincipalReturned" xlink:label="casi_InvestmentPrincipalReturned"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_InvestmentPrincipalReturned" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentPrincipal" xlink:label="casi_InvestmentPrincipal"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_InvestmentPrincipal" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentReturnPayableInInstallments" xlink:label="casi_InvestmentReturnPayableInInstallments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_InvestmentReturnPayableInInstallments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm" xlink:label="us-gaap_DebtInstrumentTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_DebtInstrumentTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TermOfAnniversaryAfterMaturityOfLoan" xlink:label="casi_TermOfAnniversaryAfterMaturityOfLoan"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_TermOfAnniversaryAfterMaturityOfLoan" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestments" xlink:label="us-gaap_ShortTermInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ShortTermInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementAmountPayable" xlink:label="casi_LicenseAgreementAmountPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementAmountPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementOneTimePaymentPayableUponCompletionOfQualityAudit" xlink:label="casi_LicenseAgreementOneTimePaymentPayableUponCompletionOfQualityAudit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementOneTimePaymentPayableUponCompletionOfQualityAudit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SublicensingRevenueFromRelatedParty" xlink:label="casi_SublicensingRevenueFromRelatedParty"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_SublicensingRevenueFromRelatedParty" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PercentageOfNetSales" xlink:label="casi_PercentageOfNetSales"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_PercentageOfNetSales" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementAggregateAmountPayableInQuarterlyInstallment" xlink:label="casi_LicenseAgreementAggregateAmountPayableInQuarterlyInstallment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementAggregateAmountPayableInQuarterlyInstallment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementAmountPayableOnCompletionOfAuditAndDeferredQuarterlyPaymentsBecomesDueImmediatelyUponEventOfNonPayment" xlink:label="casi_LicenseAgreementAmountPayableOnCompletionOfAuditAndDeferredQuarterlyPaymentsBecomesDueImmediatelyUponEventOfNonPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementAmountPayableOnCompletionOfAuditAndDeferredQuarterlyPaymentsBecomesDueImmediatelyUponEventOfNonPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CollaborativeArrangementAdditionalAmountPayable" xlink:label="casi_CollaborativeArrangementAdditionalAmountPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_CollaborativeArrangementAdditionalAmountPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CollaborativeArrangementAdditionalAmountPayableNumberOfInstallments" xlink:label="casi_CollaborativeArrangementAdditionalAmountPayableNumberOfInstallments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="22" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_CollaborativeArrangementAdditionalAmountPayableNumberOfInstallments" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCoLtdDetails" xlink:type="extended" xlink:title="40102 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (China Resources Pharmaceutical Commercial Group International Trading Co., Ltd.) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573702002"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573702002" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCo.Ltd.Member" xlink:label="casi_ChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCo.Ltd.Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_ChinaResourcesPharmaceuticalCommercialGroupInternationalTradingCo.Ltd.Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_TypeOfArrangementAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573702002"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573702002" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ExclusiveDistributionAgreementMember" xlink:label="casi_ExclusiveDistributionAgreementMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_ExclusiveDistributionAgreementMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_SubsequentEventTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_638472315573702002"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain_638472315573702002" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NonRoyaltyExclusiveDistributionPeriod" xlink:label="casi_NonRoyaltyExclusiveDistributionPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_NonRoyaltyExclusiveDistributionPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NonRoyaltyExclusiveDistributionAdditionalPeriod" xlink:label="casi_NonRoyaltyExclusiveDistributionAdditionalPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_NonRoyaltyExclusiveDistributionAdditionalPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TermOfAgreement" xlink:label="casi_TermOfAgreement"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_TermOfAgreement" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPrecisionAutoimmuneTherapeuticsCoLtdDetails" xlink:type="extended" xlink:title="40103 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (Precision Autoimmune Therapeutics Co., Ltd) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315573722008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315573722008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CasiChinaMember" xlink:label="casi_CasiChinaMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CasiChinaMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_638472315573722008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_638472315573722008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" xlink:label="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfInstallmentsForUpfrontPayment" xlink:label="casi_NumberOfInstallmentsForUpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_NumberOfInstallmentsForUpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AggregateConsiderationForEquityInvestment" xlink:label="casi_AggregateConsiderationForEquityInvestment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_AggregateConsiderationForEquityInvestment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SublicensingRevenueFromRelatedParty" xlink:label="casi_SublicensingRevenueFromRelatedParty"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_SublicensingRevenueFromRelatedParty" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsJuventasCellTherapyLtdDetails" xlink:type="extended" xlink:title="40104 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (Juventas Cell Therapy Ltd.) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573732004"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573732004" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_JuventasCellTherapyLtdMember" xlink:label="casi_JuventasCellTherapyLtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_JuventasCellTherapyLtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementMilestonePayment" xlink:label="casi_LicenseAgreementMilestonePayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementMilestonePayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MinorityInterest" xlink:label="us-gaap_MinorityInterest"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_MinorityInterest" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBioinventInternationalAbDetails" xlink:type="extended" xlink:title="40105 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (BioInvent International AB) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573742008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573742008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315573742008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315573742008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PotentialMilestonePaymentAndRoyalty" xlink:label="casi_PotentialMilestonePaymentAndRoyalty"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_PotentialMilestonePaymentAndRoyalty" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ResearchAndDevelopmentInProcess1" xlink:label="casi_ResearchAndDevelopmentInProcess1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ResearchAndDevelopmentInProcess1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquityMethodInvestmentShares" xlink:label="casi_EquityMethodInvestmentShares"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_EquityMethodInvestmentShares" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SubscriptionPeriodForWarrants" xlink:label="casi_SubscriptionPeriodForWarrants"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_SubscriptionPeriodForWarrants" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_SharePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestments" xlink:label="us-gaap_EquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_EquityMethodInvestments" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsBlackBeltTherapeuticsLimitedDetails" xlink:type="extended" xlink:title="40106 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (Black Belt Therapeutics Limited) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573772007"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573772007" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BlackBeltTherapeuticsLimitedMember" xlink:label="casi_BlackBeltTherapeuticsLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BlackBeltTherapeuticsLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PotentialMilestonePaymentAndRoyalty" xlink:label="casi_PotentialMilestonePaymentAndRoyalty"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_PotentialMilestonePaymentAndRoyalty" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementMilestonePayment" xlink:label="casi_LicenseAgreementMilestonePayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementMilestonePayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff" xlink:label="us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOff" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOffStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration" xlink:label="us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOffStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ResearchAndDevelopmentAssetAcquiredOtherThanThroughBusinessCombinationWrittenOffStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementDevelopmentMilestonePaymentPayable" xlink:label="casi_LicenseAgreementDevelopmentMilestonePaymentPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementDevelopmentMilestonePaymentPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementSalesMilestonePaymentPayable" xlink:label="casi_LicenseAgreementSalesMilestonePaymentPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementSalesMilestonePaymentPayable" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsCleaveTherapeuticsIncDetails" xlink:type="extended" xlink:title="40107 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (Cleave Therapeutics, Inc.) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573782005"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573782005" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_TypeOfArrangementAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573782005"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315573782005" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AssignmentAgreementWithCleaveMember" xlink:label="casi_AssignmentAgreementWithCleaveMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_AssignmentAgreementWithCleaveMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315573792010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315573792010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementMilestonePayment" xlink:label="casi_LicenseAgreementMilestonePayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementMilestonePayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ResearchAndDevelopmentInProcess1" xlink:label="casi_ResearchAndDevelopmentInProcess1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ResearchAndDevelopmentInProcess1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ExtinguishmentOfDebtAmount" xlink:label="us-gaap_ExtinguishmentOfDebtAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="us-gaap_ExtinguishmentOfDebtAmount" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AssignmentAgreementCommercialAndSalesMilestonePaymentsPayable" xlink:label="casi_AssignmentAgreementCommercialAndSalesMilestonePaymentsPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_AssignmentAgreementCommercialAndSalesMilestonePaymentsPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AssignmentAgreementPercentageOfRoyaltyOnNetSalesPayable" xlink:label="casi_AssignmentAgreementPercentageOfRoyaltyOnNetSalesPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_AssignmentAgreementPercentageOfRoyaltyOnNetSalesPayable" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureDescriptionOfBusinessLicenseAndDistributionAgreementsPharmathenGlobalBvDetails" xlink:type="extended" xlink:title="40108 - Disclosure - DESCRIPTION OF BUSINESS - License and Distribution Agreements (Pharmathen Global BV) (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:label="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573802011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573802011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PharmathenGlobalBvMember" xlink:label="casi_PharmathenGlobalBvMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_PharmathenGlobalBvMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" xlink:to="us-gaap_IncomeStatementLocationAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_638472315573812013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_638472315573812013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherOperatingIncomeExpenseMember" xlink:label="us-gaap_OtherOperatingIncomeExpenseMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_OtherOperatingIncomeExpenseMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:label="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_ScheduleOfDescriptionOfBusinessAndBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AdditionalMilestonePayments" xlink:label="casi_AdditionalMilestonePayments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_AdditionalMilestonePayments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NonRoyaltyExclusiveDistributionPeriod" xlink:label="casi_NonRoyaltyExclusiveDistributionPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_NonRoyaltyExclusiveDistributionPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementRefundFromTerminationOfAgreement" xlink:label="casi_LicenseAgreementRefundFromTerminationOfAgreement"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_DescriptionOfBusinessAndBasisOfPresentationLineItems" xlink:to="casi_LicenseAgreementRefundFromTerminationOfAgreement" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureSummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails" xlink:type="extended" xlink:title="40203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:label="us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:to="srt_StatementGeographicalAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain_638472315573822016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain_638472315573822016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN" xlink:label="country_CN"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CN" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK" xlink:label="country_HK"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_HK" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US" xlink:label="country_US"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_US" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="us-gaap_CashAndCashEquivalentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_CashAndCashEquivalentsLineItems" xlink:to="us-gaap_ScheduleOfCashAndCashEquivalentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CashAndCashEquivalentsLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPpeDetails" xlink:type="extended" xlink:title="40205 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - PPE (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_638472315573832010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_638472315573832010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_MachineryAndLabEquipmentMember" xlink:label="casi_MachineryAndLabEquipmentMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="casi_MachineryAndLabEquipmentMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FurnitureAndEquipmentMember" xlink:label="casi_FurnitureAndEquipmentMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="casi_FurnitureAndEquipmentMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315573832010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315573832010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentUsefulLife" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueMaxcyteIncDetails" xlink:type="extended" xlink:title="40301 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in equity securities, at fair value-MaxCyte Inc. (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573852008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573852008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_MaxcyteIncMember" xlink:label="casi_MaxcyteIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_MaxcyteIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315573852008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315573852008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentsFairValueDisclosure" xlink:label="us-gaap_EquityMethodInvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiRealizedGainLoss" xlink:label="us-gaap_EquitySecuritiesFvNiRealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquitySecuritiesFvNiRealizedGainLoss" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueBioinventInternationalAbOrdinarySharesAndWarrantsDetails" xlink:type="extended" xlink:title="40302 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in equity securities, at fair value-BioInvent International AB ordinary shares and warrants (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573862011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573862011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_MeasurementInputTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain_638472315573862011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain_638472315573862011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputPriceVolatilityMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputRiskFreeInterestRateMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315573872013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315573872013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_638472315573882014"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_638472315573882014" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquityMethodInvestmentInvestmentToBeMade" xlink:label="casi_EquityMethodInvestmentInvestmentToBeMade"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_EquityMethodInvestmentInvestmentToBeMade" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfSharesToBeSubscribed" xlink:label="casi_NumberOfSharesToBeSubscribed"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_NumberOfSharesToBeSubscribed" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfNewWarrantsSubscribed" xlink:label="casi_NumberOfNewWarrantsSubscribed"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_NumberOfNewWarrantsSubscribed" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfWarrantsSubscribedPerShare" xlink:label="casi_NumberOfWarrantsSubscribedPerShare"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_NumberOfWarrantsSubscribedPerShare" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SubscriptionPeriodForWarrants" xlink:label="casi_SubscriptionPeriodForWarrants"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_SubscriptionPeriodForWarrants" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentsFairValueDisclosure" xlink:label="us-gaap_EquityMethodInvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_WarrantsAndRightsOutstandingFairValueDisclosure" xlink:label="casi_WarrantsAndRightsOutstandingFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_WarrantsAndRightsOutstandingFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput" xlink:label="us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_WarrantsAndRightsOutstandingMeasurementInput" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UnrealizedLoss" xlink:label="casi_UnrealizedLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_UnrealizedLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiRealizedGainLoss" xlink:label="us-gaap_EquitySecuritiesFvNiRealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquitySecuritiesFvNiRealizedGainLoss" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsBioinventInternationalAbSummaryOfInvestmentsDetails" xlink:type="extended" xlink:title="40303 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - BioInvent International AB - Summary of Investments (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_638472315573912012"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_638472315573912012" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573912012"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573912012" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentOwnedAtCost" xlink:label="us-gaap_InvestmentOwnedAtCost"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_InvestmentOwnedAtCost" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="us-gaap_InvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_InvestmentsFairValueDisclosure" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsSummaryOfLongTermInvestmentsDetails" xlink:type="extended" xlink:title="40304 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Summary of Long-term investments (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfLongTermInvestmentsTable" xlink:label="casi_ScheduleOfLongTermInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfLongTermInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" priority="2" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573922011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573922011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AlestaTxMember" xlink:label="casi_AlestaTxMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AlestaTxMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="casi_ScheduleOfLongTermInvestmentsTable" xlink:to="us-gaap_InvestmentTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember_638472315573932010"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember_638472315573932010" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AvailableForSaleDebtSecuritiesMember" xlink:label="casi_AvailableForSaleDebtSecuritiesMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="casi_AvailableForSaleDebtSecuritiesMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SecuritiesMeasuredAtFairValueMember" xlink:label="casi_SecuritiesMeasuredAtFairValueMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="casi_SecuritiesMeasuredAtFairValueMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMember" xlink:label="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="casi_ScheduleOfLongTermInvestmentsTable" xlink:to="us-gaap_FinancialInstrumentAxis" priority="2" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_638472315573942008"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_638472315573942008" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConvertibleDebtMember" xlink:label="us-gaap_ConvertibleDebtMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ConvertibleDebtMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesMember" xlink:label="us-gaap_EquitySecuritiesMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_EquitySecuritiesMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsInEquityWarrantsMember" xlink:label="casi_InvestmentsInEquityWarrantsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="casi_InvestmentsInEquityWarrantsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfLongTermInvestmentsLineItems" xlink:label="casi_ScheduleOfLongTermInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_ScheduleOfLongTermInvestmentsLineItems" xlink:to="casi_ScheduleOfLongTermInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesTradingAndEquitySecuritiesFvNiCost" xlink:label="us-gaap_DebtSecuritiesTradingAndEquitySecuritiesFvNiCost"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_ScheduleOfLongTermInvestmentsLineItems" xlink:to="us-gaap_DebtSecuritiesTradingAndEquitySecuritiesFvNiCost" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" xlink:label="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_ScheduleOfLongTermInvestmentsLineItems" xlink:to="us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DebtAndEquitySecuritiesUnrealizedGainLossIncludingImpairment" xlink:label="casi_DebtAndEquitySecuritiesUnrealizedGainLossIncludingImpairment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_ScheduleOfLongTermInvestmentsLineItems" xlink:to="casi_DebtAndEquitySecuritiesUnrealizedGainLossIncludingImpairment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="us-gaap_TradingSecuritiesDebt"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_ScheduleOfLongTermInvestmentsLineItems" xlink:to="us-gaap_TradingSecuritiesDebt" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueJuventasCellTherapyLtdDetails" xlink:type="extended" xlink:title="40305 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in equity securities, at fair value-Juventas Cell Therapy Ltd. (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573962011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573962011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_JuventasCellTherapyLtdMember" xlink:label="casi_JuventasCellTherapyLtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_JuventasCellTherapyLtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeDomain_638472315573962011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeDomain_638472315573962011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PutOptionMember" xlink:label="us-gaap_PutOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:to="us-gaap_PutOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_PaymentsToAcquireEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OwnershipPercentage" xlink:label="casi_OwnershipPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_OwnershipPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionRate" xlink:label="us-gaap_RelatedPartyTransactionRate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_RelatedPartyTransactionRate" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AdditionalEquityMethodInvestmentsPurchased" xlink:label="casi_AdditionalEquityMethodInvestmentsPurchased"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_AdditionalEquityMethodInvestmentsPurchased" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentsFairValueDisclosure" xlink:label="us-gaap_EquityMethodInvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueAdjustment" xlink:label="us-gaap_AssetsFairValueAdjustment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_AssetsFairValueAdjustment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromEquityFinancing" xlink:label="casi_ProceedsFromEquityFinancing"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_ProceedsFromEquityFinancing" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyTerm" xlink:label="casi_LoansAdvancedToRelatedPartyTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MinorityInterest" xlink:label="us-gaap_MinorityInterest"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_MinorityInterest" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueAlestaTherapeuticsBvDetails" xlink:type="extended" xlink:title="40306 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in equity securities, at fair value-Alesta Therapeutics B.V. (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573982014"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315573982014" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BlackBeltTxLimitedMember" xlink:label="casi_BlackBeltTxLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BlackBeltTxLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AlestaTxMember" xlink:label="casi_AlestaTxMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AlestaTxMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_PaymentsToAcquireEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OwnershipPercentage" xlink:label="casi_OwnershipPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_OwnershipPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquityMethodInvestmentsContribution" xlink:label="casi_EquityMethodInvestmentsContribution"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_EquityMethodInvestmentsContribution" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquityMethodInvestmentsExchangeOfCommonStocks" xlink:label="casi_EquityMethodInvestmentsExchangeOfCommonStocks"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_EquityMethodInvestmentsExchangeOfCommonStocks" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FullyDilutedCapitalPercentage" xlink:label="casi_FullyDilutedCapitalPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_FullyDilutedCapitalPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentsFairValueDisclosure" xlink:label="us-gaap_EquityMethodInvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" xlink:label="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm" xlink:label="us-gaap_DebtInstrumentTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_DebtInstrumentTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoanToBeAdvanced" xlink:label="casi_LoanToBeAdvanced"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoanToBeAdvanced" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionRate" xlink:label="us-gaap_RelatedPartyTransactionRate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_RelatedPartyTransactionRate" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AdditionalEquityMethodInvestmentsPurchased" xlink:label="casi_AdditionalEquityMethodInvestmentsPurchased"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_AdditionalEquityMethodInvestmentsPurchased" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyAmountOfEqualInstallments" xlink:label="casi_LoansAdvancedToRelatedPartyAmountOfEqualInstallments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyAmountOfEqualInstallments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyPercentageOfPricePerShareIssuedAtWhichOutstandingPrincipalLoanIsToBeConverted" xlink:label="casi_LoansAdvancedToRelatedPartyPercentageOfPricePerShareIssuedAtWhichOutstandingPrincipalLoanIsToBeConverted"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyPercentageOfPricePerShareIssuedAtWhichOutstandingPrincipalLoanIsToBeConverted" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInEquitySecuritiesAtFairValueCleaveTherapeuticsIncDetails" xlink:type="extended" xlink:title="40307 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in equity securities, at fair value-Cleave Therapeutics, Inc. (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574012015"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574012015" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentInConvertibleNote" xlink:label="casi_InvestmentInConvertibleNote"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_InvestmentInConvertibleNote" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyTerm" xlink:label="casi_LoansAdvancedToRelatedPartyTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionRate" xlink:label="us-gaap_RelatedPartyTransactionRate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_RelatedPartyTransactionRate" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyConversionMinimumEquityFinancingRoundAmount" xlink:label="casi_LoansAdvancedToRelatedPartyConversionMinimumEquityFinancingRoundAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyConversionMinimumEquityFinancingRoundAmount" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LoansAdvancedToRelatedPartyConversionPercentageOfPerSharePrice" xlink:label="casi_LoansAdvancedToRelatedPartyConversionPercentageOfPerSharePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_LoansAdvancedToRelatedPartyConversionPercentageOfPerSharePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ExtinguishmentOfDebtAmount" xlink:label="us-gaap_ExtinguishmentOfDebtAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ExtinguishmentOfDebtAmount" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesRealizedGainLoss" xlink:label="us-gaap_DebtSecuritiesRealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_DebtSecuritiesRealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueAdjustment" xlink:label="us-gaap_AssetsFairValueAdjustment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_AssetsFairValueAdjustment" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureInvestmentInEquitySecuritiesAtFairValueAndLongTermInvestmentsInvestmentInPrecisionAutoimmuneTherapeuticsCoLtdPatDetails" xlink:type="extended" xlink:title="40308 - Disclosure - INVESTMENT IN EQUITY SECURITIES, AT FAIR VALUE AND LONG-TERM INVESTMENTS - Investment in Precision Autoimmune Therapeutics Co Ltd (PAT) (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsTable" xlink:label="us-gaap_ScheduleOfInvestmentsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574022015"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574022015" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CasiChinaMember" xlink:label="casi_CasiChinaMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CasiChinaMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_638472315574032015"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_638472315574032015" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" xlink:label="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AggregateConsiderationForEquityInvestment" xlink:label="casi_AggregateConsiderationForEquityInvestment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_AggregateConsiderationForEquityInvestment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PercentageOfEquityHeldInJointVenture" xlink:label="casi_PercentageOfEquityHeldInJointVenture"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_PercentageOfEquityHeldInJointVenture" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromEquityMethodInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_IncomeLossFromEquityMethodInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PercentageOfInterestInBoardSeats" xlink:label="casi_PercentageOfInterestInBoardSeats"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="casi_PercentageOfInterestInBoardSeats" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" xlink:label="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureLeasesDetails" xlink:type="extended" xlink:title="40501 - Disclosure - LEASES - (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574042014"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574042014" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CASIWuxiMember" xlink:label="casi_CASIWuxiMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CASIWuxiMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LessorOperatingLeaseTermOfContract" xlink:label="us-gaap_LessorOperatingLeaseTermOfContract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LessorOperatingLeaseTermOfContract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PrepaidOperatingLeasePayments" xlink:label="casi_PrepaidOperatingLeasePayments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_PrepaidOperatingLeasePayments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OperatingLeaseRightOfUseReturned" xlink:label="casi_OperatingLeaseRightOfUseReturned"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_OperatingLeaseRightOfUseReturned" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfOperatingLeases" xlink:label="casi_NumberOfOperatingLeases"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_NumberOfOperatingLeases" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableLeaseCost" xlink:label="us-gaap_VariableLeaseCost"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_VariableLeaseCost" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseCost" xlink:label="us-gaap_OperatingLeaseCost"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingLeaseCost" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosurePropertyPlantAndEquipmentNarrativesDetails" xlink:type="extended" xlink:title="40601 - Disclosure - PROPERTY, PLANT AND EQUIPMENT - Narratives (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574062013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574062013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_638472315574072013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_638472315574072013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_MachineryAndLabEquipmentMember" xlink:label="casi_MachineryAndLabEquipmentMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="casi_MachineryAndLabEquipmentMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FurnitureAndEquipmentMember" xlink:label="casi_FurnitureAndEquipmentMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="casi_FurnitureAndEquipmentMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentUsefulLife" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="us-gaap_DepreciationDepletionAndAmortization"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DepreciationDepletionAndAmortization" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TangibleAssetImpairmentCharges" xlink:label="us-gaap_TangibleAssetImpairmentCharges"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TangibleAssetImpairmentCharges" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureIntangibleAssetsNarrativesDetails" xlink:type="extended" xlink:title="40701 - Disclosure - INTANGIBLE ASSETS - Narratives (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574082014"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574082014" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AbbreviatedNewDrugApplicationsMember" xlink:label="casi_AbbreviatedNewDrugApplicationsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_AbbreviatedNewDrugApplicationsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FolotynMember" xlink:label="casi_FolotynMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_FolotynMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="us-gaap_OtherIntangibleAssetsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_OtherIntangibleAssetsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574092017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574092017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfAbbreviatedNewDrugApplications" xlink:label="casi_NumberOfAbbreviatedNewDrugApplications"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="casi_NumberOfAbbreviatedNewDrugApplications" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnDispositionOfIntangibleAssets" xlink:label="us-gaap_GainLossOnDispositionOfIntangibleAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_GainLossOnDispositionOfIntangibleAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_ImpairmentOfIntangibleAssetsFinitelived" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureIntangibleAssetsNetDefiniteLivedIntangibleAssetsDetails" xlink:type="extended" xlink:title="40702 - Disclosure - INTANGIBLE ASSETS - Net Definite-lived Intangible Assets (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574172011"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574172011" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AbbreviatedNewDrugApplicationsMember" xlink:label="casi_AbbreviatedNewDrugApplicationsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_AbbreviatedNewDrugApplicationsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FolotynMember" xlink:label="casi_FolotynMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_FolotynMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="us-gaap_OtherIntangibleAssetsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_OtherIntangibleAssetsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FiniteLivedIntangibleAssetsAccumulatedImpairment" xlink:label="casi_FiniteLivedIntangibleAssetsAccumulatedImpairment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="casi_FiniteLivedIntangibleAssetsAccumulatedImpairment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShortTermBorrowingsDetails" xlink:type="extended" xlink:title="40901 - Disclosure - SHORT TERM BORROWINGS (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="us-gaap_LineOfCreditFacilityTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_LineOfCreditFacilityTable" xlink:to="us-gaap_LineOfCreditFacilityAxis" priority="2" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_638472315574192016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain_638472315574192016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EastWestBankMember" xlink:label="casi_EastWestBankMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="casi_EastWestBankMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ChinaCiticBankCorporationLimitedMember" xlink:label="casi_ChinaCiticBankCorporationLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="casi_ChinaCiticBankCorporationLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_LineOfCreditFacilityTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574192016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574192016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CasiChinaMember" xlink:label="casi_CasiChinaMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CasiChinaMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="us-gaap_LineOfCreditFacilityLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_LineOfCreditFacilityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCredit" xlink:label="us-gaap_LineOfCredit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_LineOfCredit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromLinesOfCredit" xlink:label="us-gaap_ProceedsFromLinesOfCredit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_ProceedsFromLinesOfCredit" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureNotesPayableDetails" xlink:type="extended" xlink:title="41001 - Disclosure - NOTES PAYABLE (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ScheduleOfNotesPayableTable" xlink:label="casi_ScheduleOfNotesPayableTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="us-gaap_LineOfCreditFacilityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_ScheduleOfNotesPayableTable" xlink:to="us-gaap_LineOfCreditFacilityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="us-gaap_LineOfCreditFacilityLenderDomain_638472315574202013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_LineOfCreditFacilityAxis" xlink:to="us-gaap_LineOfCreditFacilityLenderDomain_638472315574202013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_MTBankMember" xlink:label="casi_MTBankMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="casi_MTBankMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NotesPayableLineItems" xlink:label="casi_NotesPayableLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_NotesPayableLineItems" xlink:to="casi_ScheduleOfNotesPayableTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_NotesPayableLineItems" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm" xlink:label="us-gaap_DebtInstrumentTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_NotesPayableLineItems" xlink:to="us-gaap_DebtInstrumentTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_NotesPayableLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NotesPayableForgiven" xlink:label="casi_NotesPayableForgiven"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_NotesPayableLineItems" xlink:to="casi_NotesPayableForgiven" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DebtInstrumentDecreaseInterestForgiveness" xlink:label="casi_DebtInstrumentDecreaseInterestForgiveness"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="casi_NotesPayableLineItems" xlink:to="casi_DebtInstrumentDecreaseInterestForgiveness" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureGrantsDetails" xlink:type="extended" xlink:title="41101 - Disclosure - GRANTS (Details)">
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_GrantsDisclosureTable" xlink:label="casi_GrantsDisclosureTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="casi_GrantsDisclosureTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574222018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574222018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CASIWuxiMember" xlink:label="casi_CASIWuxiMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CASIWuxiMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_GrantsDisclosureLineItems" xlink:label="casi_GrantsDisclosureLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="casi_GrantsDisclosureLineItems" xlink:to="casi_GrantsDisclosureTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LessorOperatingLeaseTermOfContract" xlink:label="us-gaap_LessorOperatingLeaseTermOfContract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="casi_GrantsDisclosureLineItems" xlink:to="us-gaap_LessorOperatingLeaseTermOfContract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_GrantsEligible" xlink:label="casi_GrantsEligible"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="casi_GrantsDisclosureLineItems" xlink:to="casi_GrantsEligible" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromGovernmentGrant" xlink:label="casi_ProceedsFromGovernmentGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="casi_GrantsDisclosureLineItems" xlink:to="casi_ProceedsFromGovernmentGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherIncome" xlink:label="us-gaap_OtherIncome"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="casi_GrantsDisclosureLineItems" xlink:to="us-gaap_OtherIncome" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureRedeemableNoncontrollingInterestAndLongTermBorrowingDetails" xlink:type="extended" xlink:title="41201 - Disclosure - REDEEMABLE NONCONTROLLING INTEREST AND LONG TERM BORROWING (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MinorityInterestTable" xlink:label="us-gaap_MinorityInterestTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_MinorityInterestTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574232015"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574232015" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CASIWuxiMember" xlink:label="casi_CASIWuxiMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CASIWuxiMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_WuxiLpMember" xlink:label="casi_WuxiLpMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="dei_EntityDomain" xlink:to="casi_WuxiLpMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_638472315574232015"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_638472315574232015" use="optional"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="casi_CASIWuxiMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:label="us-gaap_OptionIndexedToIssuersEquityTypeDomain_638472315574242019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeAxis" xlink:to="us-gaap_OptionIndexedToIssuersEquityTypeDomain_638472315574242019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CallOptionMember" xlink:label="us-gaap_CallOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:to="us-gaap_CallOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PutOptionMember" xlink:label="us-gaap_PutOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OptionIndexedToIssuersEquityTypeDomain" xlink:to="us-gaap_PutOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_638472315574252019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain_638472315574252019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ConvertibleLoanMember" xlink:label="casi_ConvertibleLoanMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="casi_ConvertibleLoanMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsAxis" xlink:label="us-gaap_DividendsAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_DividendsAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsDomain" xlink:label="us-gaap_DividendsDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DividendsAxis" xlink:to="us-gaap_DividendsDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsDomain" xlink:label="us-gaap_DividendsDomain_638472315574252019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DividendsAxis" xlink:to="us-gaap_DividendsDomain_638472315574252019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InstallmentOneMember" xlink:label="casi_InstallmentOneMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DividendsDomain" xlink:to="casi_InstallmentOneMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InstallmentTwoMember" xlink:label="casi_InstallmentTwoMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DividendsDomain" xlink:to="casi_InstallmentTwoMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InstallmentThreeMember" xlink:label="casi_InstallmentThreeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DividendsDomain" xlink:to="casi_InstallmentThreeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InstallmentFourMember" xlink:label="casi_InstallmentFourMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DividendsDomain" xlink:to="casi_InstallmentFourMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MinorityInterestLineItems" xlink:label="us-gaap_MinorityInterestLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_MinorityInterestTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OwnershipPercentage" xlink:label="casi_OwnershipPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_OwnershipPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentCommitment" xlink:label="casi_InvestmentCommitment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_InvestmentCommitment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InitialCashInvestment" xlink:label="casi_InitialCashInvestment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_InitialCashInvestment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SelectedAndasToBeTransferred" xlink:label="casi_SelectedAndasToBeTransferred"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_SelectedAndasToBeTransferred" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="us-gaap_PaymentsToAcquireInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_PaymentsToAcquireInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentPrincipalReturned" xlink:label="casi_InvestmentPrincipalReturned"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_InvestmentPrincipalReturned" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ReductionInRegisteredCapital" xlink:label="casi_ReductionInRegisteredCapital"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_ReductionInRegisteredCapital" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentPrincipal" xlink:label="casi_InvestmentPrincipal"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_InvestmentPrincipal" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentReturnPayableInInstallments" xlink:label="casi_InvestmentReturnPayableInInstallments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_InvestmentReturnPayableInInstallments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm" xlink:label="us-gaap_DebtInstrumentTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_DebtInstrumentTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TermOfAnniversaryAfterMaturityOfLoan" xlink:label="casi_TermOfAnniversaryAfterMaturityOfLoan"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_TermOfAnniversaryAfterMaturityOfLoan" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_DeemedDividendsAdjustment" xlink:label="casi_DeemedDividendsAdjustment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_DeemedDividendsAdjustment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent" xlink:label="us-gaap_DividendsPayableCurrentAndNoncurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_DividendsPayableCurrentAndNoncurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CallOptionToPurchaseInvestmentPeriod" xlink:label="casi_CallOptionToPurchaseInvestmentPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_CallOptionToPurchaseInvestmentPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfGuaranteeAgreements" xlink:label="casi_NumberOfGuaranteeAgreements"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="casi_NumberOfGuaranteeAgreements" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShareholdersEquityDetails" xlink:type="extended" xlink:title="41301 - Disclosure - SHAREHOLDERS' EQUITY (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_TypeOfArrangementAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315574302018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315574302018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_StockSaleAgreementMember" xlink:label="casi_StockSaleAgreementMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_StockSaleAgreementMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_OppenheimerAndCo.IncMember" xlink:label="casi_OppenheimerAndCo.IncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_OppenheimerAndCo.IncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574302018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574302018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_HcWainwrightCoLlcMember" xlink:label="casi_HcWainwrightCoLlcMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_HcWainwrightCoLlcMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockSharesAuthorized" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockCommonShares" xlink:label="us-gaap_TreasuryStockCommonShares"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockCommonShares" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:label="us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchaseProgramAuthorizedAmount1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased" xlink:label="us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedDuringPeriodValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ExcessStockSharesAuthorized" xlink:label="us-gaap_ExcessStockSharesAuthorized"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ExcessStockSharesAuthorized" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NetProceedsFromIssuanceOfCommonStock" xlink:label="casi_NetProceedsFromIssuanceOfCommonStock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_NetProceedsFromIssuanceOfCommonStock" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PublicOfferingPrice" xlink:label="casi_PublicOfferingPrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_PublicOfferingPrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureCostsOfRevenuesDetails" xlink:type="extended" xlink:title="41401 - Disclosure - COSTS OF REVENUES (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_ProductOrServiceAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain_638472315574342019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain_638472315574342019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EVOMELAMember" xlink:label="casi_EVOMELAMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ProductsAndServicesDomain" xlink:to="casi_EVOMELAMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PercentageRoyaltiesRequiredToBePaidPeriod" xlink:label="casi_PercentageRoyaltiesRequiredToBePaidPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_PercentageRoyaltiesRequiredToBePaidPeriod" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureNetLossPerShareDetails" xlink:type="extended" xlink:title="41501 - Disclosure - NET LOSS PER SHARE (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_638472315574352018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain_638472315574352018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_WarrantMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShareBasedCompensationCompensationExpenseDetails" xlink:type="extended" xlink:title="41701 - Disclosure - SHARE-BASED COMPENSATION - Compensation Expense (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_IncomeStatementLocationAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain_638472315574362020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_638472315574362020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_ResearchAndDevelopmentExpenseMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="us-gaap_SellingAndMarketingExpenseMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_SellingAndMarketingExpenseMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_GeneralAndAdministrativeExpenseMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensation" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShareBasedCompensationOptionsOutstandingDetails" xlink:type="extended" xlink:title="41703 - Disclosure - SHARE-BASED COMPENSATION - Options Outstanding (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis" xlink:label="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain" xlink:label="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis" xlink:to="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain" xlink:label="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_638472315574372020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis" xlink:to="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain_638472315574372020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityBasedArrangementsIndividualContractsTypeOfDeferredCompensationDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_638472315574372020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_638472315574372020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PerformanceBasedOptionMember" xlink:label="casi_PerformanceBasedOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="casi_PerformanceBasedOptionMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShareBasedCompensationStockOptionOutstandingDetails" xlink:type="extended" xlink:title="41704 - Disclosure - SHARE-BASED COMPENSATION - Stock Option Outstanding (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementClassOfStockAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_638472315574422019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_ClassOfStockDomain_638472315574422019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_RangeOneMember" xlink:label="casi_RangeOneMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="casi_RangeOneMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_RangeTwoMember" xlink:label="casi_RangeTwoMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="casi_RangeTwoMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_RangeThreeMember" xlink:label="casi_RangeThreeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="casi_RangeThreeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_RangeFourMember" xlink:label="casi_RangeFourMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="casi_RangeFourMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" xlink:label="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1" xlink:label="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureShareBasedCompensationDetails" xlink:type="extended" xlink:title="41705 - Disclosure - SHARE-BASED COMPENSATION (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain_638472315574452022"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain_638472315574452022" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LongTermIncentivePlan2011Member" xlink:label="casi_LongTermIncentivePlan2011Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="casi_LongTermIncentivePlan2011Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LongTermIncentivePlan2021Member" xlink:label="casi_LongTermIncentivePlan2021Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="casi_LongTermIncentivePlan2021Member" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574452022"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574452022" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_638472315574462020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_638472315574462020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TimeBasedStockOptionsMember" xlink:label="casi_TimeBasedStockOptionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="casi_TimeBasedStockOptionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PerformanceBasedOptionMember" xlink:label="casi_PerformanceBasedOptionMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="casi_PerformanceBasedOptionMember" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EstimatedShareBasedCompensationExpense" xlink:label="casi_EstimatedShareBasedCompensationExpense"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_EstimatedShareBasedCompensationExpense" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ShareBasedCompensationExpenseToBePaidOverRemainingVestingPeriod" xlink:label="casi_ShareBasedCompensationExpenseToBePaidOverRemainingVestingPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_ShareBasedCompensationExpenseToBePaidOverRemainingVestingPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensation" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedExpireTerms" xlink:label="casi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedExpireTerms"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedExpireTerms" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PerformanceShareBasedCompensationExpense" xlink:label="casi_PerformanceShareBasedCompensationExpense"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_PerformanceShareBasedCompensationExpense" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ShareBasedPaymentCashReceivedFromStockOptionExercises" xlink:label="casi_ShareBasedPaymentCashReceivedFromStockOptionExercises"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_ShareBasedPaymentCashReceivedFromStockOptionExercises" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TotalUnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod" xlink:label="casi_TotalUnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_TotalUnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod" xlink:label="casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UnrecognizedShareBasedCompensationCostExpectedToRecognizeOverWeightedAveragePeriod" xlink:label="casi_UnrecognizedShareBasedCompensationCostExpectedToRecognizeOverWeightedAveragePeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_UnrecognizedShareBasedCompensationCostExpectedToRecognizeOverWeightedAveragePeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriodRelatedToNonProbableConditionOptions" xlink:label="casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriodRelatedToNonProbableConditionOptions"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="casi_UnrecognizedShareBasedCompensationCostExpectedToBeRecognizedOverWeightedAveragePeriodRelatedToNonProbableConditionOptions" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureIncomeTaxesDetails" xlink:type="extended" xlink:title="41806 - Disclosure - INCOME TAXES (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxContingencyTable" xlink:label="us-gaap_IncomeTaxContingencyTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="us-gaap_TaxCreditCarryforwardAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_IncomeTaxContingencyTable" xlink:to="us-gaap_TaxCreditCarryforwardAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TaxCreditCarryforwardAxis" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_638472315574492020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TaxCreditCarryforwardAxis" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain_638472315574492020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchMember" xlink:label="us-gaap_ResearchMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TaxCreditCarryforwardNameDomain" xlink:to="us-gaap_ResearchMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="us-gaap_IncomeTaxAuthorityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_IncomeTaxContingencyTable" xlink:to="us-gaap_IncomeTaxAuthorityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain_638472315574492020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityDomain_638472315574492020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DomesticCountryMember" xlink:label="us-gaap_DomesticCountryMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_DomesticCountryMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ForeignCountryMember" xlink:label="us-gaap_ForeignCountryMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_ForeignCountryMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_IncomeTaxContingencyTable" xlink:to="srt_StatementGeographicalAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain_638472315574502016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain_638472315574502016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_CN" xlink:label="country_CN"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_CN" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_HK" xlink:label="country_HK"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_SegmentGeographicalDomain" xlink:to="country_HK" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_IncomeTaxContingencyTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574512020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574512020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxContingencyLineItems" xlink:label="us-gaap_IncomeTaxContingencyLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_IncomeTaxContingencyTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions" xlink:label="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PercentageOfValuationAllowanceRecognized" xlink:label="casi_PercentageOfValuationAllowanceRecognized"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="casi_PercentageOfValuationAllowanceRecognized" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_DeferredTaxAssetsLiabilitiesNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="us-gaap_OperatingLossCarryforwards"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_OperatingLossCarryforwards" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="us-gaap_TaxCreditCarryforwardAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_TaxCreditCarryforwardAmount" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_TaxCreditCarryforwardExpirationPeriod" xlink:label="casi_TaxCreditCarryforwardExpirationPeriod"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="casi_TaxCreditCarryforwardExpirationPeriod" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="us-gaap_UnrecognizedTaxBenefits"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_UnrecognizedTaxBenefits" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UnderpaymentOfTaxesStatueOfLimitationExtendedTerm" xlink:label="casi_UnderpaymentOfTaxesStatueOfLimitationExtendedTerm"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="casi_UnderpaymentOfTaxesStatueOfLimitationExtendedTerm" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureFairValueMeasurementsFinancialAndNonFinancialAssetsAndLiabilitiesDetails" xlink:type="extended" xlink:title="41901 - Disclosure - FAIR VALUE MEASUREMENTS - Financial and Non-Financial Assets and Liabilities (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574542019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574542019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_638472315574542019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_638472315574542019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574552017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574552017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ArithmeticAverageMember" xlink:label="srt_ArithmeticAverageMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_ArithmeticAverageMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MedianMember" xlink:label="srt_MedianMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MedianMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="us-gaap_InvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_InvestmentsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ShortTermInvestmentsFairValue" xlink:label="casi_ShortTermInvestmentsFairValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_ShortTermInvestmentsFairValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LongTermDepositsFairValueDisclosure" xlink:label="casi_LongTermDepositsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_LongTermDepositsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsFairValueDisclosureWarrantsMeasuredAtFairValueThroughProfitAndLoss" xlink:label="casi_InvestmentsFairValueDisclosureWarrantsMeasuredAtFairValueThroughProfitAndLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_InvestmentsFairValueDisclosureWarrantsMeasuredAtFairValueThroughProfitAndLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsFairValueDisclosureConvertibleLoan" xlink:label="casi_InvestmentsFairValueDisclosureConvertibleLoan"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_InvestmentsFairValueDisclosureConvertibleLoan" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentsFairValueDisclosureConvertibleLoanMeasuredAtFairValueThroughProfitAndLoss" xlink:label="casi_InvestmentsFairValueDisclosureConvertibleLoanMeasuredAtFairValueThroughProfitAndLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_InvestmentsFairValueDisclosureConvertibleLoanMeasuredAtFairValueThroughProfitAndLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput" xlink:label="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureFairValueMeasurementsQuantitativeInformationAboutLevel3FairValueMeasurementsDetails" xlink:type="extended" xlink:title="41902 - Disclosure - FAIR VALUE MEASUREMENTS - Quantitative Information about Level 3 Fair Value Measurements (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_638472315574582018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_638472315574582018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574582018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574582018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="us-gaap_ValuationTechniqueAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_ValuationTechniqueAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain_638472315574582018"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain_638472315574582018" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MarketApproachValuationTechniqueMember" xlink:label="us-gaap_MarketApproachValuationTechniqueMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ValuationTechniqueDomain" xlink:to="us-gaap_MarketApproachValuationTechniqueMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="srt_RangeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574622020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574622020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ArithmeticAverageMember" xlink:label="srt_ArithmeticAverageMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_ArithmeticAverageMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MedianMember" xlink:label="srt_MedianMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MedianMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput" xlink:label="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="casi_EquitySecuritiesWithoutReadilyDeterminableFairValueMeasurementInput" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="us-gaap_InvestmentsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_InvestmentsFairValueDisclosure" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureFairValueMeasurementsDetails" xlink:type="extended" xlink:title="41903 - Disclosure - FAIR VALUE MEASUREMENTS (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_638472315574642016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_638472315574642016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574642016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_638472315574642016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574652017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574652017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AbbreviatedNewDrugApplicationsMember" xlink:label="casi_AbbreviatedNewDrugApplicationsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_AbbreviatedNewDrugApplicationsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_638472315574652017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_638472315574652017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ConvertibleDebtMember" xlink:label="us-gaap_ConvertibleDebtMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ConvertibleDebtMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574662019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574662019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AlestaTxMember" xlink:label="casi_AlestaTxMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AlestaTxMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NonFinancialAssetsFairValueDisclosure" xlink:label="casi_NonFinancialAssetsFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_NonFinancialAssetsFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FairValueCarryingAmount" xlink:label="casi_FairValueCarryingAmount"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="casi_FairValueCarryingAmount" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillFairValueDisclosure" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureRelatedPartyTransactionsDetails" xlink:type="extended" xlink:title="42001 - Disclosure - RELATED PARTY TRANSACTIONS (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_TitleOfIndividualAxis" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_638472315574682017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain_638472315574682017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ChairmanAndChiefExecutiveOfficerMember" xlink:label="casi_ChairmanAndChiefExecutiveOfficerMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="casi_ChairmanAndChiefExecutiveOfficerMember" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_RangeAxis" priority="2" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember" xlink:label="srt_RangeMember_638472315574692024"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_638472315574692024" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="srt_EquityMethodInvesteeNameDomain_638472315574692024"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_638472315574692024" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" xlink:label="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="casi_PrecisionAutoimmuneTherapeuticsCo.LtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574702020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574702020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_EmergingTechnologyPartnersLLCMember" xlink:label="casi_EmergingTechnologyPartnersLLCMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_EmergingTechnologyPartnersLLCMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_JuventasCellTherapyLtdMember" xlink:label="casi_JuventasCellTherapyLtdMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_JuventasCellTherapyLtdMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="us-gaap_RelatedPartyTransactionAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="us-gaap_RelatedPartyTransactionAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RelatedPartyTransactionAxis" xlink:to="us-gaap_RelatedPartyTransactionDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="us-gaap_RelatedPartyTransactionDomain_638472315574702020"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_RelatedPartyTransactionAxis" xlink:to="us-gaap_RelatedPartyTransactionDomain_638472315574702020" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyMember" xlink:label="us-gaap_RelatedPartyMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RelatedPartyTransactionDomain" xlink:to="us-gaap_RelatedPartyMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_638472315574712013"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_638472315574712013" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CasiChinaMember" xlink:label="casi_CasiChinaMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="casi_CasiChinaMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="us-gaap_SubsequentEventTypeAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_638472315574722014"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain_638472315574722014" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_UpfrontPayment" xlink:label="casi_UpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_UpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberOfInstallmentsForUpfrontPayment" xlink:label="casi_NumberOfInstallmentsForUpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_NumberOfInstallmentsForUpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_SublicensingRevenueFromRelatedParty" xlink:label="casi_SublicensingRevenueFromRelatedParty"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_SublicensingRevenueFromRelatedParty" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromReimbursementOfLaborPreclinicalAndClinalExpense" xlink:label="casi_ProceedsFromReimbursementOfLaborPreclinicalAndClinalExpense"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_ProceedsFromReimbursementOfLaborPreclinicalAndClinalExpense" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LessorOperatingLeaseTermOfContract" xlink:label="us-gaap_LessorOperatingLeaseTermOfContract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_LessorOperatingLeaseTermOfContract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLeaseIncome" xlink:label="us-gaap_OperatingLeaseLeaseIncome"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_OperatingLeaseLeaseIncome" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment" xlink:label="us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromCollectionOfOtherReceivables" xlink:label="us-gaap_ProceedsFromCollectionOfOtherReceivables"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ProceedsFromCollectionOfOtherReceivables" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_SharePrice" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NetProceedsFromIssuanceOfCommonStock" xlink:label="casi_NetProceedsFromIssuanceOfCommonStock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="casi_NetProceedsFromIssuanceOfCommonStock" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureCommitmentsAndContingenciesDetails" xlink:type="extended" xlink:title="42101 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574752021"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574752021" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BioinventInternationalAbMember" xlink:label="casi_BioinventInternationalAbMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BioinventInternationalAbMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BlackBeltTherapeuticsLimitedMember" xlink:label="casi_BlackBeltTherapeuticsLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BlackBeltTherapeuticsLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_PharmathenGlobalBvMember" xlink:label="casi_PharmathenGlobalBvMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_PharmathenGlobalBvMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AcrotechBiopharmaL.l.c.Member" xlink:label="casi_AcrotechBiopharmaL.l.c.Member"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AcrotechBiopharmaL.l.c.Member" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_TypeOfArrangementAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315574762021"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_638472315574762021" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember" xlink:label="casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="casi_LicenseAgreementWithMundipharmaInternationalCorporationLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574772019"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_638472315574772019" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_FolotynMember" xlink:label="casi_FolotynMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="casi_FolotynMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberMilestonesAchieved" xlink:label="casi_NumberMilestonesAchieved"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_NumberMilestonesAchieved" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_NumberMilestonesPaymentsOutstanding" xlink:label="casi_NumberMilestonesPaymentsOutstanding"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_NumberMilestonesPaymentsOutstanding" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementMilestonePayment" xlink:label="casi_LicenseAgreementMilestonePayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_LicenseAgreementMilestonePayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_LicenseAgreementUpfrontPayment" xlink:label="casi_LicenseAgreementUpfrontPayment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_LicenseAgreementUpfrontPayment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AmountPayableForAdvancedProcurementOfNewActivePharmaceuticalIngredientsUponAchievementOfConditions" xlink:label="casi_AmountPayableForAdvancedProcurementOfNewActivePharmaceuticalIngredientsUponAchievementOfConditions"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="casi_AmountPayableForAdvancedProcurementOfNewActivePharmaceuticalIngredientsUponAchievementOfConditions" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedBalanceSheetsDetails" xlink:type="extended" xlink:title="42401 - Disclosure - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Balance Sheets (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedBalanceSheetStatementTable" xlink:label="srt_CondensedBalanceSheetStatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="srt_CondensedBalanceSheetStatementTable" xlink:to="srt_ConsolidatedEntitiesAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain_638472315574782021"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain_638472315574782021" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ParentCompanyMember" xlink:label="srt_ParentCompanyMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_ParentCompanyMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:label="srt_CondensedBalanceSheetStatementsCaptionsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="srt_CondensedBalanceSheetStatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_AssetsAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsCurrentAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentEquitySecuritiesFairValue" xlink:label="casi_InvestmentEquitySecuritiesFairValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="casi_InvestmentEquitySecuritiesFairValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="us-gaap_AccountsReceivableNetCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AccountsReceivableNetCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherReceivables" xlink:label="us-gaap_OtherReceivables"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_OtherReceivables" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherReceivableAfterAllowanceForCreditLossRelatedPartyTypeExtensibleEnumeration" xlink:label="us-gaap_OtherReceivableAfterAllowanceForCreditLossRelatedPartyTypeExtensibleEnumeration"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OtherReceivables" xlink:to="us-gaap_OtherReceivableAfterAllowanceForCreditLossRelatedPartyTypeExtensibleEnumeration" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoryNet" xlink:label="us-gaap_InventoryNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_InventoryNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_IntercompanyReceivables" xlink:label="casi_IntercompanyReceivables"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AssetsAbstract" xlink:to="casi_IntercompanyReceivables" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_IntangibleAssetsNetExcludingGoodwill" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermInvestments" xlink:label="us-gaap_LongTermInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_LongTermInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_InvestmentInSubsidiaries" xlink:label="casi_InvestmentInSubsidiaries"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AssetsAbstract" xlink:to="casi_InvestmentInSubsidiaries" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Assets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_IntercompanyPayablesCurrent" xlink:label="casi_IntercompanyPayablesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="casi_IntercompanyPayablesCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="us-gaap_OtherLiabilitiesNoncurrent"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_OtherLiabilitiesNoncurrent" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_Liabilities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_CommonStockValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AdditionalPaidInCapital" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_TreasuryStockValue" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfOperationsAndComprehensiveLossDetails" xlink:type="extended" xlink:title="42402 - Disclosure - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Operations and Comprehensive Loss (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedIncomeStatementTable" xlink:label="srt_CondensedIncomeStatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="srt_CondensedIncomeStatementTable" xlink:to="srt_ConsolidatedEntitiesAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain_638472315574852022"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain_638472315574852022" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ParentCompanyMember" xlink:label="srt_ParentCompanyMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_ParentCompanyMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedIncomeStatementsCaptionsLineItems" xlink:label="srt_CondensedIncomeStatementsCaptionsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="srt_CondensedIncomeStatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_Revenues" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="us-gaap_CostOfGoodsAndServicesSold"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_CostOfGoodsAndServicesSold" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GrossProfit" xlink:label="us-gaap_GrossProfit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_GrossProfit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostsAndExpensesAbstract" xlink:label="us-gaap_CostsAndExpensesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_CostsAndExpensesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_IntercompanyOperatingExpenses" xlink:label="casi_IntercompanyOperatingExpenses"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="casi_IntercompanyOperatingExpenses" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherCostAndExpenseOperating" xlink:label="us-gaap_OtherCostAndExpenseOperating"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_OtherCostAndExpenseOperating" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostsAndExpenses" xlink:label="us-gaap_CostsAndExpenses"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_CostsAndExpenses" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_OperatingIncomeLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_InterestIncomeExpenseNet" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromSubsidiariesBeforeTax" xlink:label="us-gaap_IncomeLossFromSubsidiariesBeforeTax"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_IncomeLossFromSubsidiariesBeforeTax" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="us-gaap_OtherNonoperatingIncomeExpense"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_OtherNonoperatingIncomeExpense" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:label="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss" xlink:label="us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_DebtAndEquitySecuritiesRealizedGainLoss" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="us-gaap_ProfitLoss" priority="1" use="optional"/>
</link:definitionLink>
<link:definitionLink xlink:role="http://www.entremed.com/role/DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementsOfCashFlowsDetails" xlink:type="extended" xlink:title="42403 - Disclosure - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Cash Flows (Details)">
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedCashFlowStatementTable" xlink:label="srt_CondensedCashFlowStatementTable"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="srt_CondensedCashFlowStatementTable" xlink:to="srt_ConsolidatedEntitiesAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain_638472315574882016"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain_638472315574882016" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ParentCompanyMember" xlink:label="srt_ParentCompanyMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="srt_ParentCompanyMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="srt_CondensedCashFlowStatementTable" xlink:to="srt_CounterpartyNameAxis" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574892017"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_638472315574892017" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_BlackBeltTxLimitedMember" xlink:label="casi_BlackBeltTxLimitedMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_BlackBeltTxLimitedMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_AlestaTxMember" xlink:label="casi_AlestaTxMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_AlestaTxMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_CleaveTherapeuticsIncMember" xlink:label="casi_CleaveTherapeuticsIncMember"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="casi_CleaveTherapeuticsIncMember" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:label="srt_CondensedCashFlowStatementsCaptionsLineItems"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="srt_CondensedCashFlowStatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi" xlink:label="us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan" xlink:label="casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ProceedsFromExtinguishmentOfInvestmentInConvertibleLoan" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireIntangibleAssets" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment" xlink:label="us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireInProcessResearchAndDevelopment" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="us-gaap_PaymentsToAcquireInvestments"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireInvestments" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ReceiptOfRepaymentOfConvertibleNote" xlink:label="casi_ReceiptOfRepaymentOfConvertibleNote"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="casi_ReceiptOfRepaymentOfConvertibleNote" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries" xlink:label="us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromLinesOfCredit" xlink:label="us-gaap_ProceedsFromLinesOfCredit"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromLinesOfCredit" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfNotesPayable" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="casi-20231231.xsd#casi_ProceedsFromIssuanceOfCommonStockAndWarrants" xlink:label="casi_ProceedsFromIssuanceOfCommonStockAndWarrants"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="casi_ProceedsFromIssuanceOfCommonStockAndWarrants" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockOptionsExercised" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" priority="1" use="optional"/>
<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations"/>
<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" priority="1" use="optional"/>
</link:definitionLink>
</link:linkbase>


14 Previous Filings that this Filing References

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 5/23/23  CASI Pharmaceuticals, Inc.        S-8 POS     5/23/23    3:156K                                   Toppan Merrill/FA
 4/26/23  CASI Pharmaceuticals, Inc.        20-F       12/31/22  129:16M                                    Toppan Merrill Bridge/FA
 1/31/23  CASI Pharmaceuticals, Inc.        F-4                   22:2.7M                                   Toppan Merrill/FA
11/14/22  CASI Pharmaceuticals, Inc. (DE)   10-Q        9/30/22   74:7.2M                                   Toppan Merrill Bridge/FA
 8/12/22  CASI Pharmaceuticals, Inc. (DE)   10-Q        6/30/22   76:8.1M                                   Toppan Merrill Bridge/FA
12/10/21  CASI Pharmaceuticals, Inc. (DE)   8-K:5,9    12/08/21   12:219K                                   Toppan Merrill/FA
 3/30/21  CASI Pharmaceuticals, Inc. (DE)   10-K       12/31/20  109:13M                                    Toppan Merrill Bridge/FA
11/09/20  CASI Pharmaceuticals, Inc. (DE)   10-Q        9/30/20   91:7.2M                                   Toppan Merrill/FA
 3/16/20  CASI Pharmaceuticals, Inc. (DE)   10-K       12/31/19   98:6.9M                                   Toppan Merrill/FA
 8/09/19  CASI Pharmaceuticals, Inc. (DE)   10-Q        6/30/19   75:16M                                    Toppan Merrill/FA
 5/15/19  CASI Pharmaceuticals, Inc. (DE)   10-Q        3/31/19   78:5.6M                                   Toppan Merrill/FA
 3/29/19  CASI Pharmaceuticals, Inc. (DE)   10-K       12/31/18   91:7.7M                                   Toppan Merrill/FA
 8/14/17  CASI Pharmaceuticals, Inc. (DE)   10-Q        6/30/17   40:1.7M                                   Toppan Merrill/FA
 4/17/07  CASI Pharmaceuticals, Inc.        8-K:5,8,9   4/16/07    9:152K                                   Bowne - DC/FA
Top
Filing Submission 0001558370-24-004190   –   Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)

Copyright © 2024 Fran Finnegan & Company LLC – All Rights Reserved.
AboutPrivacyRedactionsHelp — Sun., Apr. 28, 1:25:31.1pm ET