Mismatch Repair System (MMR) Status did not affect Survival in Patients with Resected Stage II Colon Cancer

ABSTRACT Background MMR has been suggested, with controversy, as a prognostic and predictive marker in stage II colon cancer. The aim of this study was to evaluate association between MMR and survival in stage II colon cancer. Methods Between January 2003 and December 2008, 860 patients with curatively resected stage II colon cancer were included. Deficient MMR (dMMR) was defined as tumors with MLH1 and/or MSH2 loss and others as proficient MMR (pMMR) by immunohistochemistry. Clinical risk (CR) factors were used for dividing patients into the high or the standard CR group. Results Of 860 patients, 14.7% showed dMMR, 42.4% had ≥1 CR factors, 85.8% patients received adjuvant chemotherapy. Age and gender were balanced with MMR status and CR. There was no difference in terms of the recurrence rate (RR), relapse-free survival (RFS) or overall survival (OS) according to either MMR status or the CR group. Among CR factors, pT4 was the only prognostic factor associated with poor OS. Adjuvant chemotherapy was associated with lower RR, better RFS and OS. By multivariate analysis, neither MMR nor CR was related to RFS or OS, while adjuvant chemotherapy was associated with better OS. The estimated cumulative incidence of recurrence after considering competing risk was not affected by MMR, CR and adjuvant chemotherapy. Conclusions MMR status did not affect RFS and OS in patients with stage II colon cancer. Only pT4 among high CR factors did influence OS. Although adjuvant chemotherapy seemed to decrease RR and improve OS by conventional survival analysis, it was not associated with the cumulative incidence of recurrence after adjusting competing risk.