Right Sided Colon Cancer as a Distinct Histopathological Subtype with Reduced Prognosis.

Background/aims: Recent data suggest that tumors of the right and left colon should be distinguished as they differ in clinical and molecular characteristics.

Methods: A total of 1,319 patients who underwent surgical resection for colon cancer (CC) were investigated. Tumors between the ileocecal valve and the hepatic flexure were classified as right CC (RCC), tumors between the splenic flexure and the rectum as left CC (LCC).

Results: RCC revealed a higher cause-specific mortality risk (hazard ratio 1.36, 95% CI 1.10-1.68, p = 0.005) and lower 5-year cause-specific (RCC 64.9%, 95% CI 60.4-69.4, LCC 70.7%, 95% CI 67.2-74.2, p = 0.032) and disease-free (RCC 56.0%, 95% CI 51.5-60.5, LCC 59.9%, 95% CI 56.2-63.6, p = 0.025) survival rates. RCCs were more often microsatellite instable (RCC 37.2%, LCC 13.0%, p < 0.001) and more often showed KRAS (RCC 42.5%, LCC 18.9%, p = 0.001) and BRAF mutations (RCC 26.6%, LCC 3.2%, p < 0.001).

Conclusion: RCC and LCC differ significantly regarding clinical, histopathological and molecular genetic features and can be considered as distinct entities. The reduced prognosis of RCC may be caused by higher rates of microsatellite instability, KRAS and BRAF mutations.