Continuation of Serplulimab Plus Chemotherapy After First Progression in Advanced Gastric or Gastro-oesophageal Junction Adenocarcinoma: an Open-label, Randomised Phase II Trial

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. never received systemic anti-tumor drug therapy before； 5. HER2 negative and PD-L1 CPS≥5; 6. Measurable lesion according to RECIST v1.1 by IRRC; 7. ECOG score 0-1; 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. Have received any research drugs within 14 days before the first use of the study drugs.