Zimberelimab Anti-PD1 +/- Domvanalimab in Resectable Mmrd Gastric Cancer

This study tests whether adding immune checkpoint drugs — zimberelimab (anti-PD1) alone or combined with domvanalimab — before surgery improves outcomes for people with resectable (surgically removable) stomach or gastroesophageal junction cancer that has a specific feature called microsatellite instability-high (MSI-H) or mismatch repair deficiency (MMRd). These cancers tend to respond especially well to immunotherapy. **You may be eligible if...** - You are 18 or older - You have confirmed stomach or gastroesophageal junction adenocarcinoma - Your cancer has been confirmed as MSI-H or MMRd - Your cancer is at a resectable stage (stage II-IIIB) with no distant spread - Your medical team believes surgery to completely remove the cancer is achievable **You may NOT be eligible if...** - Your cancer has spread to distant organs - Your cancer does not have the MSI-H/MMRd feature - You are not a surgical candidate - You have active autoimmune disease or prior immunotherapy treatment Talk to your doctor to see if this trial is right for you.