Neoadjuvant chemotherapy for colorectal cancer with synchronous and exclusive peritoneal metastasis: A comprehensive retrospective cohort study.

Abstract

169 Background: Colorectal cancer (CRC) with synchronous and exclusive peritoneal metastases (PM) is rare and associated with poor prognosis. The role and type of neoadjuvant chemotherapy (NAC) before cytoreductive surgery (CRS) remains controversial. We aimed to characterize this population and evaluate outcomes and prognostic factors after neoadjuvant chemotherapy. Methods: We conducted a retrospective study of CRC patients with isolated synchronous PM (2016–2021) who received NAC followed by surgical reassessment. The primary endpoint was overall survival (OS). Prognostic factors included the peritoneal cancer index (PCI) and Peritoneal Regression Grading Score (PRGS). Results: Eighty-one patients were included (median follow-up 80.7 months). NAC regimens were FOLFOX (70%), FOLFIRI (12%), or FOLFIRINOX (17%); 54% also received targeted therapy (43% anti-EGFR, 57% anti-VEGF). CRS was performed in 54 patients (65%), with complete cytoreduction (R0) achieved in 94%, and median PCI to 10 (0-39). CRS significantly improved mOS (44.1 vs 22.8 months; HR 0.27, 95% CI 0.14 0.53, p<0.001); 5-year OS was 31.1% vs 14.9% without surgery. Twenty-seven patients (33%) did not undergo CRS after NAC. Higher post-NAC PCI predicted worse OS (HR 1.64 per 5-point increment, p=0.027). PRGS showed prognostic relevance with a median OS 54.9 months (PRGS 1–2) vs 34.5 months (PRGS 3–4) (HR 2.83; 95% CI 1.0-8.04; p = 0.051). Conclusions: In CRC patients with isolated PM, complete CRS is a key survival factor. When optimal cytoreduction was not feasible during surgery, survival results were better than incomplete cytoreduction (R1 or R2), based on literature. Neoadjuvant chemotherapy guided by PRGS may help identify candidates for surgery and adjuvant therapy. Further trials are needed to define optimal regimens and personalize strategies based on PRGS or PCI.