Unveiling the prognostic significance of malignant ascites in advanced gastrointestinal cancers: a marker of peritoneal carcinomatosis burden

Background: Ascites is common in advanced gastrointestinal cancers with peritoneal metastases (PM) and negatively impacts patient survival. No study to date has specifically evaluated the relationship between ascites, PM and survival outcomes in metastatic colorectal cancer (mCRC) and metastatic gastric cancer (mGC). Objectives: This study aims to investigate and elucidate the relationship between malignant ascites, PM and survival outcomes in both mCRC and mGC patients. Design: This is a retrospective analysis of prospectively collected clinical trial data of mCRC and mGC patients with PM. Methods: We performed two pooled analyses, firstly of two Italian randomized trials enrolling patients with mCRC eligible for systemic therapy (TRIBE2; VALENTINO), and secondly of gastric cancer and peritoneal metastasis (GCPM) patients who underwent bi-directional therapeutic treatment comprising systemic and peritoneal-directed therapies. Results: Of 900 mCRC patients, 39 (4.3%) had PM with malignant ascites. Compared to the group without PM, median progression-free and overall survival were significantly inferior in the ascites group (hazard ratio (HR) for progression-free survival (PFS) 1.68, 95% confidence interval (CI): 1.21–2.35, p = 0.007; HR for overall survival (OS) 2.14, 95% CI: 1.57–3.01, p