Locoregional Control from Complete Peritoneal Cytoreduction in Patients with Extraperitoneal Colorectal Cancer Metastases: An Entropy Balanced Analysis

PURPOSE: We evaluated the role of complete cytoreductive surgery (CRS) for locoregional disease control in patients with colorectal cancer with peritoneal metastases (CRC-PM) and concurrent extraperitoneal metastases (EPM). METHODS: Institutional data identified patients with CC-0/1 CRS for CRC-PM. Patients with peritoneal disease only (PDO) were compared with those with concomitant EPM. Co-primary outcomes were progression-free survival (PFS) and peritoneal progression-free survival (p-PFS). The secondary outcome was overall survival (OS). Covariate imbalance was addressed using entropy balancing. Survival was analyzed using a weighted Cox proportional hazards model. Subgroup analyses were performed to identify favorable prognostic groups. RESULTS: In total, 83 patients were included: 31 (37.4%) had EPM. Baseline characteristics were comparable. Within the EPM cohort, liver-only metastases were most common (58%), followed by lung-only metastases (26%). EPM were managed at index CRS in 61%, before CRS in 19%, and deferred or untreated in 19% of patients. Unadjusted analyses demonstrated comparable median OS (PDO vs. EPM: 39 vs. 34 months, p = 0.551) and median p-PFS (PDO vs. EPM: 17 vs. 15 months, p = 0.346) but longer median PFS in the PDO group (14 vs. 5 months, p