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.