External validation of the Pre-operative Predictive (PROP) score for feasibility of complete cytoreduction in colorectal peritoneal metastases: a single-centre experience

Abstract Purpose Colorectal peritoneal metastases (PM) remain a major therapeutic challenge. Cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) offers prolonged survival in selected patients. Accurate preoperative assessment of resectability is crucial to avoid non-beneficial surgery. The Preoperative Predictive Score (PROP) integrates nine preoperative clinical and radiologic parameters to predict the completeness of cytoreduction (CC). This study aimed to externally validate the PROP Score in an independent European single-centre cohort. Methods 63 Patients undergoing CRS ± HIPEC for colorectal PM between 2012 and 2022 were retrospectively analysed. PROP scores were calculated from preoperative data and compared with intraoperative CC scores (CC-0, CC-1, CC-2/3). Statistical analysis included χ², Spearman correlation, and receiver operating characteristic (ROC) curve evaluation. Results Sixty-three patients were included (CC-0 = 41; CC-1 = 13; CC-2/3 = 9). Median PROP values increased with lower resectability (3.4 vs. 7.2 vs. 10.8; p < 0.001). A cutoff ≥ 6 predicted incomplete cytoreduction with 78% sensitivity and 90% specificity (AUC = 0.919). PROP correlated strongly with the Peritoneal Cancer Index (ρ = 0.673; p < 0.001). No 30- or 90-day mortality was observed. Conclusion The PROP Score reliably predicts the likelihood of complete cytoreduction in colorectal PM using solely preoperative parameters. Moreover it is the first score which is able to preoperatively discriminate patients with a future CC-0 und CC-1 resection. Its external validation supports evidence-based patient selection for CRS ± HIPEC, optimizing surgical decision-making and resource utilization.