Association Between Prognosis and Tumor Laterality in Early-Stage Colon Cancer.

Importance: Recent data have suggested that disease biology and outcome of colon cancer may differ between right-sided and left-sided tumors. However, the literature on the prognostic value of tumor laterality is conflicting.

Objective: To explore differences in laterality based on disease characteristics and outcomes in a population-based cohort of early-stage colon cancer.

Design, Setting, and Participants: This investigation was a population-based retrospective cohort study of patients with early-stage colon cancer from the province of Ontario, Canada. Electronic records of treatment were linked to the Ontario Cancer Registry to identify all patients with colon cancer who underwent resection between January 1, 2002, and December 31, 2008. The date of the final analysis was October 20, 2016. The study population included a 25% random sample of all patients with resected stage I to III disease. Right-sided colon cancer was defined as any tumor arising in the cecum, ascending colon, hepatic flexure, or transverse colon. Left-sided colon cancer was defined as any tumor arising in the splenic flexure, descending colon, sigmoid colon, or rectosigmoid colon.

Main Outcomes and Measures: Overall survival (OS) and cancer-specific survival (CSS) measured from the time of resection.

Results: This study identified 6365 patients with early-stage colon cancer (48.7% [3098 of 6365] female). Their median age was 72 years, and 51.7% (3291 of 6365) had right-sided disease. Stage distribution was 18.3% (1163 of 6365) stage I, 38.4% (2446 of 6365) stage II, and 43.3% (2756 of 6365) stage III. Patients with right-sided colon cancer were more likely to be older (median age, 73 vs 70 years; P < .001) and female (54.4% [1790 of 3291] vs 42.6% [1308 of 3074], P < .001) and have greater comorbidity. Right-sided cancers were more likely to be T4 (19.2% [631 of 3291] vs 15.9% [490 of 3074], P < .001) and poorly differentiated (21.1% [695 of 3291] vs 9.6% [295 of 3074], P < .001) but less likely to be node positive (42.0% [1383 of 3291] vs 44.7% [1373 of 3074], P = .03) compared with left-sided disease. In adjusted analyses, there was no difference in long-term survival for right-sided compared with left-sided colon cancer: the hazard ratios were 1.00 (95% CI, 0.92-1.08) for OS and 1.00 (95% CI, 0.91-1.10) for CSS. These results were consistent when the survival analyses were restricted to stage III disease: the hazard ratios were 1.03 (95% CI, 0.93-1.14) for OS and 1.10 (95% CI, 0.97-1.24) for CSS.

Conclusions and Relevance: In this population-based cohort of early-stage resected colon cancer, disease laterality was not associated with long-term OS or CSS.