A Study of Pembrolizumab With Trastuzumab and Chemotherapy in People With Esophagogastric Cancer

This study tests whether adding pembrolizumab (an immunotherapy drug) to the standard combination of trastuzumab (a HER2-targeted drug) and chemotherapy can improve outcomes for people with HER2-positive stomach or esophageal cancer when given before and after surgery. **You may be eligible if...** - You are 18 or older with HER2-positive stomach, gastroesophageal junction, or esophageal cancer - Your cancer is confirmed HER2-positive by a tissue biopsy test (IHC3+ or IHC2+/FISH) - Your cancer can be completely removed with surgery - You have not received any prior treatment for this cancer - Your blood counts, kidney, and liver function are adequate **You may NOT be eligible if...** - Your cancer has spread to other parts of the body (metastatic) - You have previously received HER2-targeted therapy or immunotherapy (anti-PD-1/PD-L1) - You have received any prior treatment for this esophageal or gastric cancer Talk to your doctor to see if this trial is right for you.