Mismatch Repair Status and Surgical Outcomes in Localized Colorectal Cancer: A Nationwide Cohort Study

This study examined the association between deficient mismatch repair (dMMR) versus proficient MMR (pMMR) status and overall survival and disease-free survival in patients with localized colorectal cancer. Several distinctions exist between patients with dMMR and pMMR colorectal cancer. However, the impact on prognosis is yet to be investigated in large-scale cohort studies. In this cohort study, we included patients who underwent curative-intent surgery for localized colorectal cancer between 2009 and 2020. Patients were identified in the Danish Colorectal Cancer Group database and patient-level data were extracted from 6 registry databases. After inclusion, patients with dMMR status were matched 1:1 to patients with pMMR status using an estimated propensity score. After matching, 5994 patients were included. The patients had a median age of 74 years and a median follow-up of 4.1 years. There was no significant association between mismatch repair (MMR) status and overall survival (hazard ratio, 0.91; 95% confidence interval [CI], 0.81-1.03) or disease-free survival (hazard ratio, 0.89; 95% CI, 0.78-1.01). However, the restricted 5-year mean disease-free survival time, calculated due to violation of the proportional hazards assumption, showed a significant absolute difference of 0.13 years (95% CI, 0.03-0.23; = 0.01) in favor of the dMMR group. No significant association with overall survival was found according to MMR status. dMMR status was, however, found to be associated with marginally improved disease-free survival compared to pMMR status in patients with localized colorectal cancer undergoing curative-intent surgery.