[Evaluation of BRAF V600E Mutations in High-Level Microsatellite Instability(MSI-H)Colon Cancer - Comparison Between Genetic Testing and Immunohistochemical Staining].

BRAF V600E mutation plays an important role in the serrated neoplasia pathway of colorectal tumorigenesis and is a negative predictive factor for chemotherapy response as well as a prognostic factor in patients with colorectal cancer. To evaluate BRAF V600E mutations, a conventional polymerase chain reaction(PCR)is performed but recently immunohistochemistry (IHC)with a BRAF antibody has been used. Although similarities between the PCR and IHC methods have been reported, some investigators have doubts about the usefulness of IHC for BRAF mutation analysis. The subjects were 38 colorectal cancer patients with tumors demonstrating loss of both MLH1 and PMS2, and high-level microsatellite instability. Of the original 39 patients, 1 was excluded due to Lynch syndrome, which was identified using germline mutation testing. The mutation rate of BRAF V600E was 57.9% using both methods, but the concordance rate was 68.4%, with a kappa-value of 0.33. We should consider the usefulness of the IHC method in the evaluation of BRAF mutations in colorectal cancer patients.