First-line Treatment With RC48 Plus Sintilimab and S-1 in Advanced Gastric Cancer (RCTS2)

This study is testing a combination of three treatments — RC48 (a targeted antibody-drug), sintilimab (an immunotherapy), and S-1 (a chemotherapy pill) — as a first treatment option for people with advanced stomach or esophageal junction cancer. **You may be eligible if...** - You are 18–75 years old - You have been diagnosed with advanced or metastatic stomach or gastroesophageal junction cancer that cannot be surgically removed - Your tumor tests HER2-positive - You have not received prior systemic treatment, or you received chemotherapy that finished more than 6 months ago and the cancer has returned - You are in generally good functional condition (able to carry out light activity) - Your organs (liver, kidneys, blood) are functioning adequately - Your life expectancy is at least 3 months **You may NOT be eligible if...** - You have brain metastases or cancer that has spread to the lining of the brain - You have a history of autoimmune disease, organ transplant, or HIV - You have active severe infections (including tuberculosis) - You have uncontrolled lung disease, heart disease, or poorly managed chronic conditions - You have had major surgery in the past 28 days - You have another active cancer Talk to your doctor to see if this trial is right for you.