Comparing the Efficacy and Safety of Chemotherapy Combined With or Without Immunotherapy as Postoperative Adjuvant Regimens in Patients With Resectable Gastric Cancer/Adenocarcinoma of the Esophagogastric Junction After Radical Surgery

Inclusion Criteria: 1. Age ≥ 18 years old, gender not restricted; 2. Subjects diagnosed with gastric cancer (GC) or gastroesophageal junction cancer (GEJC) through imaging and other examinations, and with histopathological diagnosis of adenocarcinoma; 3. HER2 overexpression or amplification results are negative; 4. After radical surgery treatment, the investigator assesses that further adjuvant treatment is necessary, and the adjuvant treatment plan must be the one specified in this protocol. Exclusion Criteria: 1. Gastric cancer that is known to be squamous cell carcinoma, undifferentiated carcinoma, or of other tissue types, or gastric cancer that is adenocarcinoma mixed with other tissue types; 2. Within 3 months before adjuvant therapy, there was a significant clinically significant bleeding symptom or a clear bleeding tendency; 3. Within 6 months before adjuvant therapy, had suffered from intestinal obstruction and/or had clinical signs or symptoms of digestive tract obstruction, including incomplete obstruction related to the original disease or requiring routine parenteral hydration, parenteral nutrition, or tube feeding; 4. Within 5 years before starting adjuvant therapy, was diagnosed with a malignant tumor (excluding malignant tumors with low metastasis and mortality risks, such as: skin basal cell carcinoma or cervical carcinoma in situ that has been adequately treated); 5. Within 30 days before starting adjuvant therapy, had participated in other clinical studies and used study drugs containing active ingredients;