Mismatch repair status predicts survival after adjuvant treatment in stage II colon cancer patients

Abstract Background and Objectives Stage II colon cancer is primarily a surgical disease. Only a still not well‐defined subset of patients may benefit from postoperative adjuvant chemotherapy. The relationship between adjuvant chemotherapy and survival after relapse is furthermore still not definitely explored in this group of patients. A number of reports suggest some association between defective mismatch repair (dMMR) and colorectal cancer stage II prognosis, but due to contradictory results from existing studies, the exact predictive role is still not fully understood. Methods Retrospective multicenter study including 451 stage II colon cancer patients. The proficiency or deficiency of mismatch repair was tested using immunohistochemistry and analyzed in relationship to two survival outcomes: overall survival (OS) and postrelapse survival. Results Patients with dMMR (20.4%) derived no OS benefit from adjuvant chemotherapy (hazard ratio [HR], 1.05; 95% confidence interval [CI], 0.47‐2.38; P = .897). Patients with proficient mismatch repair (pMMR) tumors receiving adjuvant chemotherapy had the significantly better OS in comparison to those not receiving chemotherapy (HR, 0.54; 95% CI, 0.35‐0.82; P = .004). This relationship remained significant in multivariable analysis (HR, 0.42; 95% CI, 0.22‐0.78; P = .007). Patients with pMMR relapsing after adjuvant treatment lived significantly longer than those relapsing without previous adjuvant treatment (HR, 0.55; 95% CI, 0.32‐0.96; P = .033) and this result remained significant in the multivariable model (HR, 0.49; 95% CI, 0.26‐0.93; P = .030). Conclusion In stage II CC patients, adjuvant chemotherapy improves therapeutic outcomes only in patients with pMMR tumors. Survival after relapse in patients having received adjuvant chemotherapy is significantly longer for patients with pMMR. No survival benefit from adjuvant chemotherapy was seen among patients with dMMR tumors.