Prognostic impact of high-risk factors and KRAS mutation in patients with stage II deficient mismatch repair colon cancer: a retrospective cohort study

Background: Deficient mismatch repair (dMMR) is associated with a good prognosis in patients with stage II colon cancer and observation is recommended after surgery in these patients. In contrast, patients with high-risk factors and Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation is associated with a poor prognosis in colon cancer. However, the prognosis and treatment of patients with dMMR colon cancer combined with high-risk factors or KRAS mutation remains unclear. This study aimed to evaluate whether patients with dMMR colon cancer combined with high-risk factors or KRAS mutation require further treatment. Methods: This single-center retrospective study included patients who received radical surgical resection and mismatch repair (MMR) immunohistochemical detection at The Sixth Affiliated Hospital of Sun Yat-sen University between May 2011 and March 2021. The high-risk factors and KRAS mutation were assessed by clinicopathological data and targeted sequencing. Associations with disease-free survival (DFS) were evaluated using multivariable Cox models. Results: Among the 1,357 patients with stage II colorectal cancer included, 226 of these patients had dMMR. Patients in the dMMR group were more likely to be younger [<50 years: odds ratio (OR) =0.401, 95% CI: 0.288-0.558, P<0.001], with poor differentiation (OR =5.800, 95% CI: 3.437-9.787, P<0.001), no perineural invasion (OR =0.132, 95% CI: 0.047-0.368, P<0.001), and more than 12 excised lymph nodes (OR =0.427, 95% CI: 0.188-0.968, P=0.042). The disease-free survival (DFS) of patients with stage II dMMR colon cancer with high-risk factors was similar to that of patients without high-risk factors (hazard ratio (HR) =1.285, 95% CI: 0.273-6.051, P=0.607). A total of 836 patients had complete data regarding KRAS status. Compared with KRAS wild-type patients, patients with KRAS gene mutation had a trend of poor prognosis in patients with stage II colon cancer (HR=1.483, 95% CI: 0.983-2.239, P=0.061). In addition, dMMR appeared to be a protective factor in patients with KRAS mutation (HR =0.138, 95% CI: 0.019-1.002, P=0.0501). Conclusions: The survival of patients with stage II dMMR colon cancer with high-risk factors was similar to that of patients without high-risk factors, regardless of the presence of KRAS mutation.