Background : The search for high-risk factors in stage II colon cancer (CC) is ongoing and several high-risk factors for stage II CC have been identified; however, the effects of tumor sidedness on prognosis is not clear. This study aims to determine whether tumor sidedness could be identified as another high-risk factor for stage II CC. Methods : We retrospectively analyzed 189 patients with stage II CC, following consecutive curative resection surgery performed between 2008 and 2014. We compared clinicopathological findings and long-term outcomes between the patients with right colonic cancer (RCC) and patients with left colonic cancer (LCC). Prognostic factors for survival were determined using univariate and Cox proportional regression analyses. Results : A total of 72 patients were diagnosed with RCC and 117 patients were diagnosed with LCC. Patients with RCC were significantly older (p < 0.001) than those with LCC, and the number of harvested lymph nodes (HLNs) was greater in the RCC group (RCC: 25 vs. LCC: 19; p = 0.003). The overall survival (OS) was notably worse in the RCC group than the OS in the LCC group (5 year survival rate—RCC: 81.3% vs. LCC: 90.4%; p = 0.025), whereas no significant difference was observed in disease-free survival (5 year survival rate—RCC: 74.8% vs. LCC: 83.4%; p = 0.065). Cox proportional regression analysis showed that tumor sidedness (hazard ratio (HR): 3.78, 95% confidence interval (CI): 1.61–8.85, p = 0.022), gender (HR: 3.27, 95% CI: 1.27–8.47, p = 0.014), and the number of HLNs (HR: 4.58, 95% CI: 1.95–10.74, p < 0.001) were independent prognostic factors for OS. Conclusion : Patients with a right-sided primary tumor location have more negative prognostic factors and worse long-term outcomes than those with a left-sided primary tumor location in stage II CC. Tumor sidedness is a high-risk factor in stage II CC patients.
