Defective Mismatch Repair Status was not Associated with DFS and OS in Stage II Colon Cancer Treated with Adjuvant Chemotherapy.

ABSTRACT

BACKGROUND: Mismatch repair (MMR) status has been proposed, with some controversy, as a prognostic and predictive marker in stage II colon cancer. The aim of this study was to evaluate the association between MMR and survival in stage II colon cancer. METHODS: A total of 860 patients with curatively resected stage II colon cancer were selected for inclusion between January 2003 and December 2008. Tumors lacking expression of MLH1 and/or MSH2, as determined by immunohistochemistry, were classified as having deficient MMR (dMMR), whereas other tumors were classified as having proficient MMR (pMMR). Clinical risk (CR) factors were used to divide patients into high or standard CR groups. RESULTS: Of 860 patients, 14.7 % were dMMR, 42.4 % had ≥1 CR factors, and 85.8 % patients received adjuvant chemotherapy. MMR status did not affect disease-free survival (DFS; hazard ratio [HR] 1.191, p = 0.415) or overall survival (OS; HR 1.300, p = 0.344). Among CR factors, only pathologic T4 disease tended to associate with poor OS (HR 1.979, p = 0.071). Adjuvant chemotherapy was associated with better DFS (HR 0.393, p < 0.0001) in patients with pMMR tumors. However, in patients with dMMR tumors, adjuvant chemotherapy was not associated with DFS. CONCLUSIONS: MMR status did not affect DFS or OS in patients with stage II colon cancer. In patients treated with adjuvant chemotherapy, dMMR was not associated with DFS and OS. However, adjuvant chemotherapy was associated with improved DFS in pMMR patients.