Association of Clinicopathologic and Molecular Markers on Stage-specific Survival of Right Versus Left Colon Cancer

We performed a large retrospective study of the National Cancer Database to investigate the possible underlying factors associated with the poorer survival seen in right-sided colon cancer compared with left-sided colon cancer. Right-sided colon cancer patients were older, had more biologically aggressive tumors, and a greater incidence of microsatellite instability and KRAS mutations, which more profoundly affected survival, especially in later disease stages. Background: Previous studies have shown that variability in molecular markers correlates with poorer survival outcomes in patients with right-sided colon cancer (RCC) compared with left-sided colon cancer (LCC). However, several studies have shown conflicting results when examined stage for stage. We examined RCC and LCC to assess for differences in histopathologic features and overall survival (OS). Materials and Methods: The National Cancer Database was used to identify patients with RCC and LCC from 2004 to 2013. A propensity-adjusted analysis evaluating the association between the primary site and OS was performed. Results: Of the 422,443 patients identified, 54.7% had RCC and 45.3% had LCC. For all stages, the patients with RCC were older, had more poorly differentiated tumors, and had a greater degree of microsatellite instability compared with those with LCC. Patients with RCC also had more KRAS mutations than did those with LCC. RCC patients had poorer 3- and 5-year OS at all stages, especially stage 3 (62% vs. 73% and 50% vs. 62%, respectively; P < .001). The median OS was 77.5 months for LCC and 62.3 months for RCC (P < .001). Conclusion: The present study is one of the largest studies demonstrating that RCC and LCC are different biologic entities. Patients with RCC had significantly greater rates of microsatellite instability for all stages, which has been previously shown to be prognostically advantageous. However, the results of the present study showed poorer OS at every disease stage for RCC compared with LCC. These factors have important implications for the further use of targeted therapies in the treatment of advanced colon cancer. (C) 2018 Elsevier Inc. All rights reserved.