Comparing the Efficacy and Safety of Chemotherapy Combined With or Without Immunotherapy as an Adjuvant Treatment After Radical Surgery for Patients With Resectable Adenocarcinoma of the Esophagogastric Junction of Gastric Cancer

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. Subjects who have received neoadjuvant chemotherapy for GC/GEJC before, and have undergone at least 3-4 cycles; 5. 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;