Anti-PD-1 in Combination With Systemic Chemotherapy With Nab-paclitaxel Intraperitoneal Infusion for Untreated Advanced Gastric Cancer With Malignant Ascites

This prospective observational study aims to evaluate the efficacy and safety of anti-PD-1 therapy combined with systemic chemotherapy and intraperitoneal nab-paclitaxel as first-line treatment for patients with advanced gastric or gastroesophageal junction (GC/GEJ) adenocarcinoma with malignant ascites. The study will also explore potential predictive biomarkers of treatment response through longitudinal collection and multi-omics analysis of tumor tissue, peripheral blood, and ascites.

Inclusion Criteria: \- Have fully understood the study and voluntarily signed the informed consent form (ICF); Histologically confirmed gastric adenocarcinoma or gastroesophageal junction (GC/GEJ) adenocarcinoma with unresectable advanced or metastatic disease; HER2-negative and mismatch repair-proficient (pMMR); Moderate or greater volume of ascites at baseline; Peritoneal metastasis confirmed by ascites cytology or laparoscopy; Aged 18 to 75 years, regardless of sex; Receiving first-line anti-PD-1 immunotherapy combined with systemic chemotherapy and intraperitoneal nab-paclitaxel. Exclusion Criteria: \- History of or concurrent active malignancy other than gastric cancer within the past 5 years; Previous systemic treatment for unresectable advanced or metastatic GC/GEJ adenocarcinoma.