Original StudyThe Prognostic Relevance of Histological Subtype in Patients With Peritoneal Metastases From Colorectal Cancer: A Nationwide Population-Based Study

BackgroundWith evolving treatment possibilities for peritoneal metastases (PM) from colorectal cancer (CRC), adequate prognostication and patient selection for treatment becomes increasingly important. We investigated the prognostic relevance of commonly identified histological subtypes in PM of CRC (adenocarcinoma [AC], mucinous AC [MC], and signet-ring cell carcinoma [SC]), which is currently unclear.Patients and MethodsThis study involved 4277 patients diagnosed with synchronous PM from CRC between 2005 and 2012 in The Netherlands. Kaplan-Meier analysis and log-rank testing were performed to estimate survival. Subsequently a Cox proportional hazard model was used to calculate hazard ratios for the risk of death.ResultsMost of the CRC patients were diagnosed with AC (n = 3008; 70%), whereas MC and SC were found in 958 (22%) and 311 (7%) patients, respectively. SC was associated with the highest risk of death in colon and rectal cancer, with median survival rates of respectively, 6.6 and 6.9 months. For MC, median survival varied from 10.9 months in colon and 9.8 months in rectal cancer (P > .05). In colon cancer, MC was associated with a significantly lower risk of death compared with AC (hazard ratio, 0.9; 95% confidence interval, 0.79-0.95). In rectal cancer, no such effect was observed. AC was associated with a significantly poorer survival rate in the case of primary colonic tumor localization (7.4 months in colon vs. 10.9 months in rectal cancer).ConclusionHistological subtype is an important prognostic factor in patients with synchronous PM of colorectal origin. This knowledge will aid clinicians in counseling of patients and clinical decision-making regarding possible treatment options.