This study is looking at how a combination of treatments works for patients with a type of stomach cancer. The treatments are **pembrolizumab** (a monoclonal antibody that helps the immune system fight cancer), **capecitabine** (a chemotherapy drug that stops cancer cells from growing), and **radiation therapy** (high-energy x-rays to kill cancer cells). The study will see how well these treatments work together and check for any side effects. Patients will receive pembrolizumab every 3 weeks and may also have surgery and radiation.
- **Study Length**: Treatment up to 1 year, with follow-ups for a few more years.
- **Visits**: Regular visits for treatment and check-ups.
- **Risks**: Possible side effects from drugs and radiation.
To participate, patients must have a specific type of stomach cancer that can be operated on, and they must meet certain health criteria. They cannot have other serious health issues, be pregnant, or be breastfeeding. This study aims to improve how stomach cancer is treated and support patients in their recovery.