HS-20093 in Patients With Advanced Gastric and Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: 1. At least age of 18 years at screening, with no restrictions on gender. 2. Signed and dated Informed Consent Form. 3. Participants with pathologically or cytologically confirmed locally advanced unresectable or metastatic GC/GEJC, who have failed, or intolerant to standard therapies. 4. At least one extra measurable lesion according to RECIST 1.1. 5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0\~1. 6. Estimated life expectancy \>12 weeks. 7. Agree to provide fresh or archival tumor tissue. 8. Good organ function. 9. Female subjects must not be pregnant at screening or have evidence of non-childbearing potential. 10. Men or women should be using adequate contraceptive measures throughout the study. Exclusion Criteria: 1. Treatment with any of the following: * Previous or current treatment with B7-H3 targeted therapy. * Previous or current treatment with topoisomerase I inhibitors. * Any cytotoxic chemotherapy, investigational agents and anticancer drugs within 14 days prior to the first scheduled dose of HS-20093 * Prior treatment with a monoclonal antibody within 28 days prior to the first scheduled dose of HS-20093 * Local radiotherapy for palliation within 2 weeks of the first dose of study drug, or patients received more than 30% of the bone marrow irradiation, or large-scale radiotherapy within 4 weeks prior to the first scheduled dose of HS-20093 * Treatment with drugs that are predominantly CYP3A4 strong inhibitors or inducers or sensitive substrates of CYP3A4 with a narrow therapeutic range within 7 days of the first dose of study drug; or requiring treatment with these drugs during the study. * Currently receiving drugs known to prolong QT interval or may cause torsade de pointe; or requiring treatment with these drugs during the study. 2. Histology shows squamous cell carcinoma, undifferentiated carcinoma, or mixed tumors , such as adenosquamous carcinoma or other mixed tumors. 3. Any unresolved toxicities from prior therapy greater than Grade 1 according to CTCAE 5.0 or baseline status. 4. Presence of pleural effusion/ascites requiring clinical intervention. 5. Newly diagnosed brain metastases without treatment, or brain metastases that have not achieved stability despite treatment; presence of leptomeningeal metastasis or brainstem metastasis; presence of spinal cord compression. 6. History of other primary malignancies 7. Evidence of cardiovascular risk. 8. Severe, uncontrolled or active cardiovascular diseases. 9. Severe or poorly controlled hypertension. 10. Severe or poorly controlled diabetes. 11. Poorly controlled cancer-related pain. 12. The presence of active infectious diseases has been known: hepatitis B, hepatitis C and HIV. 13. Major surgery within 4 weeks prior to the first scheduled dose of HS-20093. 14. Active infection requiring therapeutic intravenous antibiotics within 2 weeks prior to the first dose. 15. Clinically significant bleeding symptoms or marked hemorrhagic tendency within 1 month prior to the first dose of HS-20093. 16. Serious arterial or venous thromboembolic events occurring within 3 months prior to the first dose of HS-20093. 17. Active tuberculosis. 18. History of known interstitial pneumonia or immune-mediated pneumonitis. 19. History of active or prior autoimmune disease requiring systemic treatment. 20. Severe malnutrition. 21. Current hepatic encephalopathy, hepatorenal syndrome, or cirrhosis ≥ Child-Pugh class B. 22. Requires long-term glucocorticoid therapy. 23. Having undergone any major surgery within 4 weeks prior to the first dose. 24. Vaccination within 4 weeks prior to the first dose of HS-20093. 25. History of severe allergy. 26. Previous history of serious neurological or mental disorders. Unlikely to comply with study procedures, restrictions, and requirements in the opinion of the investigator. 27. Currently enrolled in or participating in any other clinical study involving investigational interventions or other types of interventional medical research.