Survival of Colon Cancer in a Population‐Based Cohort Study: A Comprehensive Analysis of Location of the Primary Tumor

ABSTRACT

Disparities in survival between left‐ versus right‐sided colon cancer have been reported. We studied the role of sidedness on survival of colon cancer across tumor biomarkers subgroups in a population‐based cohort established using the Geneva Cancer Registry database. Our study included 3503 colon cancer cases diagnosed between 1985 and 2013. Right‐sided colon cancers (ICD‐O codes C18.0, C18.2–18.4) and left‐sided colon cancers (ICD‐O codes C18.5–18.7) were compared. Five‐year net survival was estimated using the Pohar‐Perme estimator. Flexible hazard models evaluated the association of survival with sidedness adjusted for patient, tumor, and treatment characteristics. Left‐sided colon cancers were more frequent than right‐sided colon cancers (53% vs. 47%). Right‐sided colon cancer cases were older and more often women, less frequently of stage I or well differentiated. Left‐sided colon cancer had a higher 5‐year net survival than right‐sided colon cancer (66% vs. 59%, p  < 0.001). In a multivariable model, patients with a left‐sided tumor had a 25% reduction in 5‐year mortality compared with right‐sided tumors (excess hazard ratio [eHR]: 0.75, 95% confidence interval [CI]: 0.63–0.89, p  = 0.001). This association remained significant only among stage IV while not among stages I‐III. Among a subgroup of 2438 cases, stratification on tumor molecular biomarkers confirmed the better prognosis of left‐sided colon cancer versus right‐sided colon cancer among microsatellite stable (MSS) tumors, tumors with BRAF wild‐type (BRAFwt), and iCMS2 tumors. This study shows the importance of sidedness for prognosis and treatment considerations in addition to tumor biomarkers. Further research is needed to assess the molecular mechanisms underlying these differences between left and right colon cancer to address the prognostic gap.