Development of a Prognostic Nomogram for Patients with Peritoneally Metastasized Colorectal Cancer Treated with Cytoreductive Surgery and HIPEC.

BACKGROUND: With the introduction of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC), long-term survival can be achieved in selected patients with colorectal peritoneal metastases (PM). Patient selection and outcome may be improved significantly with a tool that adequately predicts survival in these patients. This study was designed to validate the peritoneal surface disease severity score (PSDSS) in patients with colorectal PM treated with CRS + HIPEC. If performance of the PSDSS was suboptimal (c < 0.7), we aimed to develop a new prognostic model. METHODS: Patients were included if they had colorectal PM and underwent CRS + HIPEC with intended complete cytoreduction in a Dutch tertiary hospital between 2007 and 2015. Statistical analyses were performed with R-software. RESULTS: A total of 200 patients underwent CRS + HIPEC. External validation of the PSDSS showed a Harrell's c statistic of 0.62. After analysis, four parameters appeared prognostically relevant factors for overall survival: age, PCI score, locoregional lymph node status, and signet ring cell histology. The weighted relevance of these parameters was turned into a prognostic nomogram that we termed colorectal peritoneal metastases prognostic surgical score (COMPASS). The COMPASS differentiated well and showed a Harrell's c statistic of 0.72 with a calibration plot showing good agreement. CONCLUSIONS: This study externally validated the PSDSS and developed a new prognostic score, the COMPASS. This pre-cytoreduction nomogram was more accurate than PSDSS in predicting survival of patients undergoing CRS + HIPEC. It can be used as tool to assist in the decision about continuing cytoreduction and HIPEC and can provide valuable information in the follow-up period after CRS + HIPEC.