HLX07+HLX10+Chemotherapy or HLX07 Monotherapy in Patients With Advanced Metastatic Gastric Cancer

Inclusion Criteria: 1. Volunteer to participate in this clinical study; completely understand and know this study as well as sign the informed consent form (ICF); be willing to follow and be able to complete all study procedures; 2. Age ≥ 18 years and ≤ 75 years when ICF is signed; 3. Unresectable locally advanced, or metastatic gastric cancer including gastroesophageal junction cancer, and histopathologically confirmed diagnosis of adenocarcinoma; 4. Arm A: never received systemic anti-tumor drug therapy before, with HER2 negative and PD-L1 CPS≥5; Arm B: failed to prior systemic anti-tumor therapy (at least 2 lines); 5. Measurable lesion according to RECIST v1.1 by IRRC; 6. ECOG score 0-1; 7. Expected survival 12 weeks. Exclusion Criteria: 1. Has other active malignancies within 5 years before the first administration of the study drug; 2. Plan to or have previously received organ or bone marrow transplantation; 3. Uncontrollable pleural effusion, pericardial effusion or ascites requiring repeated drainage; 4. Arm A: previously received antibody drugs against immune checkpoints (such as PD-1, PD-L1, CTLA4, etc.) and / or antibody drugs against EGFR; Arm B: previously received antibody drug treatment against EGFR; 5. Have received any research drugs within 14 days before the first use of the study drugs.