Exploratory Single-arm, Single-center Adjuvant Treatment of Stage IIIB-IIIC Gastric Cancer With Combination of Palizumab and SOX Regimen

This study is testing whether adding an immunotherapy drug (palizumab) to standard chemotherapy (SOX regimen) helps prevent stomach cancer from coming back after surgery in patients with advanced-stage disease. **You may be eligible if...** - You are 18–75 years old - You had surgery to remove stomach or esophageal-stomach junction cancer that was classified as stage IIIB or IIIC - Your tumor has certain molecular markers: high microsatellite instability (MSI-H), high tumor mutation burden (TMB-H), or high PD-L1 expression - You have not previously received immunotherapy for cancer - You are in generally good health and your blood counts and organ function are within normal ranges **You may NOT be eligible if...** - You have severe high blood pressure that is hard to control - You have trouble swallowing or have a blockage in your digestive tract - You have serious liver, kidney, heart, or lung disease - You have a neurological or psychiatric condition - You are currently pregnant or breastfeeding - You are enrolled in another cancer treatment trial Talk to your doctor to see if this trial is right for you.