Prognostic value of DNA mismatch repair status and KRAS mutations in Korean colorectal cancer patients.

697 Background: The association of DNA mismatch repair (MMR) and KRAS mutation on clinical outcome of patients with colorectal cancer are frequently documented. However, development of more accurate prediction on clinical outcome using combination of both biomarkers remains a worthy area of investigation. The aim of this study was to evaluate the clinical relevance of KRAS mutation and MMR status in Korean patients with colorectal cancer (CRC). Methods: Clinical and pathological information for 1174 patients, who underwent surgery for colorectal cancer in 3 teaching hospitals from 2011 to 2013, were reviewed and recorded. Mutation analysis for exon 2 of KRAS gene was performed by Sanger sequencing. Expression of MMR proteins including MLH1 and MSH2 was evaluated by immunohistochemistry. Results: The overall frequencies of KRAS mutation was 34.9%. Mutations in KRAS codon 12 and codon 13 were detected in 26.7% and 8.2% of patients, respectively. Overall, 90 s (7.7%) tumors that had at least loss of expression for at least one MMR protein were defined as MMR protein deficient (MMR-D), and the remaining tumors were classified as MMR protein intact (MMR-I). According to KRAS mutation and MMR status, CRC was classified to 4 groups: Group 1, KRAS-mutated and MMR-I; Group 2, KRAS-mutated and MMR-D; Group 3, KRAS wild and MMR-I; and Group 4, KRAS wild and MMR-D. We found that patients in Group 4 had the best prognosis, and patients in Group 2 had the worst overall survival. KRAS mutation was independently associated with shorter time to recurrence and poorer overall survival. Conclusions: Combination status of KRAS mutation and MMR provide fundamental genetic signatures affecting tumor behavior, and may be used as a prognostic biomarker for CRC patient. These findings should be validated by further larger prospective study. [Table: see text]