A population-based study on the prognostic impact of primary tumor sidedness in patients with peritoneal metastases from colon cancer.

Primary tumor location is an established prognostic factor in patients with (metastatic) colon cancer. Colon tumors can be divided into left-sided and right-sided tumors. The aim of this study was to determine the impact of primary tumor location on treatment and overall survival (OS) in patients with peritoneal metastases (PM) from colon cancer. This study is a retrospective, population-based cohort study. Records of patients diagnosed with colon cancer and synchronous PM, from 1995 through 2016, were retrieved from the Netherlands Cancer Registry (NCR). Data on diagnosis, staging, and treatment were extracted from the medical records by specifically trained NCR personnel. Information on survival status was updated annually using a computerized link with the national civil registry. In total, 7930 patients were included in this study; 4555 (57.4%) had a right-sided and 3375 (42.6%) had a left-sided primary tumor. In multivariable analysis right-sided primary tumor was associated with worse OS (HR: 1.11, 95% CI 1.03-1.19, P = .007). Of all patients diagnosed with PM, 564 (7.1%) underwent cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). Patients with left-sided primary tumors were more often candidates for CRS-HIPEC (6.5% vs. 8.0%, P = .008). OS of patients with right- and left-sided tumors who underwent CRS-HIPEC did not significantly differ. In conclusion, primary right-sided colon cancer was an independent prognostic factor for decreased OS in patients diagnosed with synchronous PM. In patients treated with CRS-HIPEC location of the primary tumor did not influence survival.