Quadrant-Specific Distribution of Peritoneal Metastases as a Prognostic Factor in Colorectal Cancer Treated with CRS and HIPEC

Background: Peritoneal metastasis (PM) from colorectal cancer (CRC) carries a poor prognosis. The Peritoneal Cancer Index (PCI) is among the principal prognostic stratification tools, yet the prognostic value of the anatomical distribution of disease beyond total PCI is underexplored. This pilot study evaluated whether quadrant-specific involvement adds prognostic information in patients undergoing cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC), with a focused analysis of oligometastatic disease (PCI ≤ 6). Methods: A single-institution cohort of 48 CRC-PM patients treated with CRS + HIPEC was analyzed. Primary endpoints were OS, DFS, and PRFS, with a focused evaluation of the oligometastatic subset (PCI ≤ 6). Comparative statistics used Student’s two-sample t test for continuous variables and chi-square or two-sided Fisher’s exact tests for categorical variables. Survival was estimated by Kaplan–Meier with log-rank tests, and prognostic factors were evaluated using Cox regression. Results: Median follow-up was 177 months (IQR 87–224). Outcomes favored PCI ≤ 6: 5-year OS and DFS were 54% and 37.5% versus 6.6% and 0% for PCI > 6, and median OS 64 vs. 29 months (log-rank p = 0.007), median DFS 30 vs. 7 months (p = 0.0002), and median PRFS 26 vs. 8 months (p = 0.0002). In the PCI ≤ 6 subset (n = 27), quadrant 3 (left upper quadrant) was associated with higher recurrence risk and shorter DFS, remaining independently prognostic for DFS (p = 0.005) and PRFS (p = 0.005). For PRFS, quadrants 7 and 8 also showed associations on univariable analysis; Q7 remained independent (p = 0.047), whereas Q8 was borderline (p = 0.077). A histology-related signal at Q8 (p = 0.011) was exploratory due to very small mucinous and signet-ring strata. Sidedness and synchronicity yielded no significant differences in quadrant involvement within PCI ≤ 6. No quadrant effects were observed in PCI > 6. Conclusions: PCI remains the dominant prognostic determinant after CRS + HIPEC, yet in oligometastatic disease, the anatomical distribution adds complementary prognostic information, particularly involvement of Q3 and Q7. These findings are hypothesis-generating and warrant validation in larger, preferably multicenter cohorts with standardized quadrant mapping. If confirmed, quadrant-directed operative planning, including consideration of prophylactic resection in selected high-risk regions, could be prospectively evaluated.