Different Cycles of Neoadjuvant PD-1 Blockades + Chemotherapy for Advanced Gastric Cancer

This study compares different numbers of chemotherapy plus immunotherapy cycles given before surgery (neoadjuvant therapy) to patients with advanced, but resectable, stomach cancer or cancer where the stomach meets the food pipe (gastroesophageal junction). Researchers want to find the optimal number of treatment cycles for the best surgical outcomes. **You may be eligible if...** - You are between 18 and 90 years old - You have been diagnosed with stomach cancer or gastroesophageal junction cancer confirmed by biopsy - Imaging or surgical evaluation has confirmed the cancer can be removed with surgery - You received at least one cycle of a PD-1 checkpoint inhibitor (immunotherapy) combined with chemotherapy before surgery - You then had radical (complete) stomach cancer surgery (gastrectomy) **You may NOT be eligible if...** - You had prior chemotherapy, radiation, or immunotherapy before this treatment - You have had another cancer in the last 5 years - You have serious underlying medical conditions Talk to your doctor to see if this trial is right for you.