Colon and rectal peritoneal carcinomatosis: are we mixing apples with oranges? A propensity score-matched analysis.

Rectal cancer is universally considered a different disease entity as compared to colon cancer, except when dealing with colorectal peritoneal carcinomatosis (PC), in which the two cancers are deemed as the same one. The present study aims to investigate the influence of primary tumor location (colon vs. rectum) on oncologic outcomes in patients undergoing cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) for colorectal peritoneal metastases. Data from three referral centers undergoing CRS plus HIPEC for PC of colorectal origin were prospectively collected. The primary outcomes were overall survival (OS) and disease-free survival (DFS) according to primary tumor location (colic vs. rectal). Univariate and multivariate analyses were performed using the Cox proportional hazard model first on the total number of patients. Then, a propensity score matching using the nearest-neighbour method with a 1:1 ratio was performed. The study included 167 patients: 126 colic and 41 rectal PC. After propensity score matching, rectal primary tumor location was independently predictive of a lower DFS (HR 1.91; 95%CI 1.06-3.45; p = 0.031) but not of a lower OS (HR 1.12; 95%CI 0.57-2.21; p = 0.73). Post-matching 3-year DFS rates were 49.2% (95%CI 34,3-70,5%) and 19.4% (95%CI 9,4-40,2%) for colic and rectal PC, respectively. The present study shows a significantly worse DFS for rectal cancer PC undergoing CRS and HIPEC compared to colon cancer PC, suggesting a possible need for dedicated pathways for rectal PC patients and posing a question for rectal PC to be considered as a unique disease entity.