Randomized Phase III Trial of mFOLFIRINOX vs. FOLFOX With Nivolumab

This study is being done to answer the following question: Can we extend your life after the diagnosis of your cancer in the stomach, esophagus, or gastroesophageal junction by adding a third chemotherapy drug to the usual combination of two chemotherapy drugs? We are doing this study because we want to find out if this approach is better or worse than the usual approach for treatment of your cancer in the stomach, esophagus, or gastroesophageal junction. The usual approach is defined as care most people get for cancer in the stomach, esophagus, or gastroesophageal junction.