M108 Plus CAPOX Versus Placebo Plus CAPOX as First-line Treatment for Claudin (CLDN) 18.2-Positive, HER2-Negative, PD-L1 CPS<5, Locally Advanced Unresectable or Metastatic Gastric or Gastroesophageal Junction (GEJ) Adenocarcinoma.

This trial is testing whether adding M108 — a new experimental drug targeting Claudin 18.2, a protein found on some stomach cancer cells — to standard CAPOX chemotherapy improves outcomes compared to chemotherapy alone for people with advanced stomach or gastroesophageal junction cancer. **You may be eligible if...** - You are between 18 and 75 years old with locally advanced unresectable or metastatic stomach or gastroesophageal junction (GEJ) cancer confirmed by biopsy - Your tumor tests positive for Claudin 18.2 expression - Your tumor is HER2-negative and has low PD-L1 expression (CPS less than 5) - You have not received prior chemotherapy for your advanced/metastatic disease - You have adequate organ function and performance status of 0-1 **You may NOT be eligible if...** - Your tumor is HER2-positive or Claudin 18.2-negative - You have had prior radiotherapy within 4 weeks of starting the study - You are pregnant or breastfeeding - You have uncontrolled infections or significant heart disease Talk to your doctor to see if this trial is right for you.