External validation of prognostic scores and comparison of predictive accuracy for patients with colorectal cancer with peritoneal metastases considered for cytoreductive surgery and intraperitoneal chemotherapy.

Background And Objectives: Prognostic scores are developed to facilitate the selection of patients with colorectal cancer peritoneal metastases (CRPM) for treatment with cytoreductive surgery (CRS) ± intraperitoneal chemotherapy (IPC). Three prominent prognostic scores are the Peritoneal Surface Disease Severity Score (PSDSS), the Colorectal Peritoneal Metastases Prognostic Surgical Score (COMPASS), and the modified COloREctal-Pc (mCOREP). We externally validate these scores and compare their predictive accuracy.

Methods: Data from consecutive CRPM patients who underwent CRS/IPC from 1996 to 2018 was used to externally validate COMPASS, PSDSS, and mCOREP. Analysis evaluated the efficacy of each score in predicting (1) open-close laparotomy-those found at laparotomy to not be eligible for curative intent CRS/IPC, (2) surgical futility-those who underwent open-close laparotomy, palliative debulking surgery, or had an overall survival of less than 12 months, and (3) overall and recurrence-free survival (OS, RFS).

Results: Prognostic scores were calculated for the 174-patient external validation cohort. COMPASS was most accurate in predicting open-close laparotomy, futile surgery, and survival (OS and RFS). Area under the curve (AUC) for open-close prediction was 0.78 (95% confidence interval, CI: 0.68-0.87), representing useful discrimination. However, AUC for futility prediction was 0.62 (95% CI: 0.52-0.71), and C-statistic for OS was 0.65 indicating only possibly helpful discrimination. C-statistic for RFS was 0.59 indicating poor discrimination.

Conclusion: While COMPASS showed the best statistical behavior, accuracy for several clinically relevant outcomes remains low, and thus applicability to clinical practice limited.