First-Line and Neoadjuvant Immunotherapy for Gastric Cancer

This study is collecting data on patients with advanced gastric (stomach) cancer who are receiving immunotherapy as their first treatment or before surgery (neoadjuvant). The goal is to better understand how immunotherapy works in real-world settings for this cancer type. **You may be eligible if...** - You are 18 or older - You have been diagnosed with advanced or locally advanced gastric cancer - You have not yet received any cancer treatment (chemotherapy, immunotherapy, etc.) - You are planned to receive immunotherapy as first-line or pre-surgical treatment - You are in good general health (ECOG 0-1) and your organs function adequately **You may NOT be eligible if...** - You have a medical reason that prevents you from receiving immunotherapy - You have already received prior cancer treatments - You have an active autoimmune disease, HIV, or a history of organ or stem cell transplant - You have an active serious infection, including tuberculosis, requiring treatment Talk to your doctor to see if this trial is right for you.