Systemic Application of Cadonilimab, LM-302, and S-1 Combined With Intraperitoneal Infusion of Paclitaxel for the Treatment of Claudin 18.2-positive Gastric Cancer With Peritoneal Metastasis

This trial is testing a combination of four cancer drugs — including immunotherapy (cadonilimab), an antibody-drug conjugate (LM-302), an oral chemotherapy (S-1), and a chemotherapy given into the belly (paclitaxel) — for people with stomach cancer that has spread to the lining of the abdomen and tests positive for a protein called Claudin 18.2. **You may be eligible if...** - You are 18 or older - You have confirmed stomach (gastric) adenocarcinoma that is HER2-negative and Claudin 18.2 positive - The cancer has spread to the peritoneum (abdominal lining) confirmed by laparoscopy - You have not had surgery to remove the stomach tumor or metastases - You are in reasonably good health (ECOG score 0 or 1) - Your life expectancy is more than 3 months **You may NOT be eligible if...** - The cancer has spread beyond the abdomen (e.g., to the liver or lungs) - You previously received immunotherapy (PD-1/PD-L1) or Claudin 18.2 targeted therapy - You are pregnant, recently gave birth, or are breastfeeding - You have severe heart disease, kidney problems, or active autoimmune disease - You have bowel obstruction or nerve damage Talk to your doctor to see if this trial is right for you.