A Study of Zolbetuximab Together with Pembrolizumab and Chemotherapy in Adults with Gastric Cancer

The goal of this research study is to test a new study treatment for a specific type of stomach cancer. It is focused on people whose tumors are CLDN18.2 positive, PD-L1 positive, and HER2 negative. This new study treatment has 3 parts: 1. A study drug called zolbetuximab 2. Another study drug called pembrolizumab 3. Standard chemotherapy (mFOLFOX or CAPOX) Researchers want to know if this combination is safe and if it works better than current treatments for people living with this specific type of stomach cancer