• Shahid Ahmed, Punam Pahwa, Duc Le, Haji Chalchal, Selliah Chandra-Kanthan, Nayyer Iqbal, and Anthony Fields.
• Saskatoon Cancer Canter, Saskatchewan Cancer Agency, Saskatoon, SK, Canada; Division of Oncology, University of Saskatchewan, Saskatoon, SK, Canada. Electronic address: shahid.ahmed@saskcancer.ca.
• Clin Colorectal Cancer. 2018 Jun 1; 17 (2): e201-e206.

BackgroundRecent evidence from clinical trials suggests that primary tumor location in patients with metastatic colorectal cancer correlates with differential outcomes, and patients with tumors originating in the right side of the colon have inferior survival. We conducted a large population-based cohort study using individual patient data to confirm the prognostic importance of primary tumor location in the general population with metastatic colorectal cancer.MethodsA cohort of 1947 patients who were diagnosed with metastatic colorectal cancer from 1992 to 2010 was studied. Ascending and transverse colon cancers were defined as right-sided tumors. Cox proportional multivariate analyses were done to determine prognostic significance of primary tumor location.ResultsThe median age was 70 years (interquartile range, 60-78 years), and the male to female ratio was 1.3:1. Twenty-nine percent had World Health Organization performance status of > 1. Seven-hundred and seventy (39%) patients had right-sided tumors, and 908 (47%) received chemotherapy. The median overall survival of patients with right-sided tumors was 14 months (95% confidence interval [CI], 12.7-15.3 months) compared with 20.5 months (95% CI, 18.5-22.5 months) of patients with left-sided tumors (P < .001). On multivariate analysis, right-sided tumors (hazard ratio [HR], 1.40; 95% CI, 1.20-1.60), no metastasectomy (HR, 2.40; 95% CI, 1.90-2.90), intact primary tumor (HR, 1.60; 95% CI, 1.32-1.90), an elevated carcinoembryonic antigen level (HR, 1.54; 95% CI, 1.30-1.90), lack of combination chemotherapy (HR, 1.52; 95% CI, 1.31-1.80), stage IVb disease (HR, 1.50; 95% CI, 1.17-1.86), leukocytosis (HR, 1.44; 95% CI, 1.28-1.73), and World Health Organization performance status > 1 (HR, 1.30; 95% CI, 1.10-1.55) were correlated with inferior survival.ConclusionsOur results confirm that individuals with metastatic colorectal cancer and right-sided tumors who received chemotherapy have inferior survival independent of other known prognostic variables. Future studies are required to understand the underlying pathophysiology.Copyright © 2017 Elsevier Inc. All rights reserved.

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