Multi-omics Based Prediction of Treatment Response to Immunotherapy Combined with Chemotherapy in Advanced Gastric/Gastroesophageal Junction Cancer.

This study is collecting comprehensive molecular data (genetics, proteins, metabolism markers) from people with advanced stomach or gastroesophageal junction cancer to predict who will respond best to immunotherapy combined with chemotherapy. **You may be eligible if...** - You are between 18 and 75 years old - You have been diagnosed with advanced or metastatic stomach or gastroesophageal junction cancer that cannot be removed by surgery - Your tumor tests negative for HER2 - You have not received any prior anti-cancer treatment - Your planned treatment is chemotherapy combined with immunotherapy - Your life expectancy is at least 3 months **You may NOT be eligible if...** - You have another active cancer, or cancer spread from another organ to your stomach - You have previously had surgery, radiation, chemotherapy, or immunotherapy for this cancer - You have a serious active infection - You have severe heart, liver, or kidney disease - You are pregnant or breastfeeding - Your tumor is HER2-positive Talk to your doctor to see if this trial is right for you.