The main objective of this study is to compare the efficacy of HS-20093 with standard of care (SOC) on prolonging overall survival (OS) in subjects with relapsed small cell lung cancer (SCLC).

This is a phase 3, randomized, open-label, multicenter study comparing HS-20093 with topotecan in patients with limited or extensive SCLC that had disease progression on or after first-line platinum-based regimen. Subjects will be randomized by a ratio of 1:1 to receive HS-20093 or topotecan until disease progression.

The primary objective of this study is to assess whether treatment with HS-20093 prolongs OS compared with treatment of topotecan among subjects with relapsed SCLC.

The secondary objectives of the study are to further evaluate the efficacy/safety of HS-20093. The exploratory objectives are to characterize the pharmacokinetics of HS-20093, evaluate E-R relationship, immunogenicity of HS-20093, B7-H3 protein expression and soluble B7-H3 expression.

Inclusion Criteria:

1. Male or female subjects ≥18 years of age.
2. Histologically or cytologically confirmed SCLC.
3. Subjects who progressed on or after first-line platinum-based regimens.
4. Has at least 1 measurable lesion as defined per RECIST 1.1.
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
6. Minimum life expectancy of more than 12 weeks.
7. Females subjects must not be pregnant at screening or have evidence of non-childbearing potential.
8. Men or women should be using adequate contraceptive measures throughout the study.
9. Subject has provided informed consent/assent prior to initiation of any study specific activities/procedures.

Exclusion Criteria:

1. Combined SCLC, any previous diagnosis of transformed SCLC or SCLC that has transformed to NSCLC.
2. Chemotherapy-free interval ≤30 days.
3. Has received prior treatment with anti-B7 homologue 3 (B7-H3) targeted agents.
4. Has received prior treatment with topoisomerase I inhibitor, including ADC that consists of topoisomerase I inhibitor.
5. Has inadequate washout period before randomization as specified in the protocol.
6. Untreated or symptomatic brain metastases with exceptions defined in the protocol.
7. Unresolved toxicity from prior anti-tumor therapy, defined as not having resolved to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 grade 1 with exceptions defined in the protocol.
8. History of other malignancy with exceptions defined in the protocol.
9. Inadequate bone marrow reserve or organ dysfunction.
10. Evidence of cardiovascular risks.
11. Severe, uncontrolled or active cardiovascular diseases.
12. Severe or uncontrolled diabetes.
13. Severe or uncontrolled high blood pressure.
14. Clinically significant bleeding or obvious bleeding tendency within 1 month before randomization.
15. Severe arterial or venous thromboembolic events within 3 months prior to randomization.
16. Severe infections within 4 weeks before randomization.
17. Receiving systemic corticosteroid therapy within 30 days prior to randomization with exceptions defined in the protocol.
18. The presence of active infectious diseases before randomization.
19. Current hepatic encephalopathy, hepatorenal syndrome, or Child-Pugh Grade B or more severe cirrhosis.
20. History of interstitial lung disease, immunotherapy-induced pneumonitis, clinically moderate or severe pulmonary disease.
21. History of severe neuropathy or mental disorders.
22. Female subjects of childbearing potential; female subjects who are breastfeeding or who plan to breastfeed while on study; female subjects planning to become pregnant while on study.
23. Vaccination or hypersensitivity of any level within 4 weeks before randomization.
24. History of severe hypersensitivity reaction, severe infusion reaction or allergy to recombinant human or mouse derived proteins.
25. Hypersensitivity to any ingredient of HS-20093, DNA topoisomerase I inhibitor or regimens of Topotecan.