The clinical benefit of a near complete cytoreduction in patients with colorectal peritoneal metastases: a propensity score matched study.

[BACKGROUND] Colorectal cancer with peritoneal metastases (PM) presents a significant therapeutic challenge. Cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) is one option to prolong survival. While completeness of cytoreduction (CC) score 0 is associated with improved outcomes, the clinical value of near-complete CC-score 1 versus open-close laparotomy (CC-3) remains unclear.

[METHODS] This retrospective study evaluates overall survival (OS) in patients with colorectal cancer PM scheduled for CRS and HIPEC from 23 global peritoneal-surface oncology centers from 2006 to 2023. A propensity score matching was performed using tumor location (colon/rectum), lymph node status, liver metastases, signet-ring histology, preoperative chemotherapy, peritoneal cancer index, and treatment year. Matching was performed using the nearest neighbor method with a caliper of 0.1, chosen after several iterations to optimize intergroup balance. Balance was assessed using standardized mean differences. Sensitivity analyses with alternative calipers and multivariable Cox regression in the unmatched cohort were considered to test the robustness of the findings. The study time-period was divided into 4 equal quartiles for analysis.

[RESULTS] In the unmatched cohort (n = 284), patients with CC-1 had significantly longer median OS compared to those with CC-3 (22.2 vs. 9.4 months, p < 0.001). After 1:1 matching (n = 172), the OS advantage of CC-1 persisted, with a median OS of 18.9 months (95 % CI: 14.2-24.7) versus 10.5 months (95 % CI: 9.4-12.3) for CC-3, p < 0.0001, HR 0.4 (95 % CI:0.27-0.56). Multivariable Cox regression confirmed CC-1 as a significant predictor of survival (HR: 0.15, 95 % CI: 0.08-0.26). The CC-1 proportion went from 55 to 65 % in time-periods 1 & 2-39 % in period 3, to 11 % in period 4; leading to significantly reduced survival rates in the latter time-periods 3 & 4.

[DISCUSSION] Near complete cytoreduction is associated with improved overall survival compared to open-close laparotomy. Prospective or standardized multicenter analyses will be required to confirm the clinical value of a near complete cytoreduction.