This study compares two treatments for people with advanced stomach or esophageal cancer. Pumitamig and Nivolumab are medicines used along with chemotherapy, which is a treatment using special drugs to kill cancer cells. "Advanced" or "metastatic" means the cancer has spread to other parts of the body.

To join, you must have not had previous treatments for this cancer, and your cancer cannot have a protein called HER2 (Human Epidermal Growth Factor Receptor 2). You also need a test result showing your cancer's PD-L1 status, which relates to how the cancer might respond to certain treatments.

People with untreated brain metastases or serious heart problems cannot join. The study checks if these treatments are safe and how well they work. "RECIST" is a way to measure if cancer is getting smaller.

• The study involves comparing two treatment combinations.
• Participants must have specific medical test results to join.
• Certain health conditions or recent surgeries might prevent participation.