Epithelial mesenchymal transition in an advanced BRAF mutation type colorectal cancer.

693 Background: BRAF mutation is associated with poor survival in colorectal cancer. We aimed to generate genomic signature associated with BRAF mutation that possibly predict prognosis in colorectal cancer. Methods: A gene expression signature reflecting BRAF mutation was generated in TCGA cohorts (n = 207). The colorectal cancer patients were stratified into two groups according to this signature: BRAF mutation type colorectal cancer or BRAF wild type colorectal cancer. Prognostic significance of BRAF mutation-associated gene signature was tested in three independent cohorts (GSE 17536, GSE 14333, and GSE 39582). Results: The BRAF mutation signature was associated with poor prognosis in two independent cohorts (total n = 522). BRAF mutation type colorectal cancer was associated with poor disease-free survival (median: not reached, P = 0.0303) in GSE14333, and associated with poor overall survival (BRAF mutation vs. wild, P = 0.0355), poor disease-free survival (P = 0.00794), and poor disease-specific survival (P = 0.0341) in GSE 17536. In GSE 39582, BRAF mutation type colorectal cancer demonstrated the trend of poor overall survival according to increase of stage. In a multivariate analysis, BRAF mutation gene signature was independent poor prognostic factor for disease-free survival (hazard ratio 2.7; 95% CI 1.59-2.83: P = 0.001). Gene network analyses suggested epithelial-mesenchymal transition and colon cancer metastasis signaling are the possible explanations for poor prognosis of BRAF mutation type colorectal cancer. Conclusions: BRAF mutation signature is highly associated with poor prognosis in colorectal cancer, especially in advanced stage, and the molecules associated with epithelial-mesenchymal transition can be potential therapeutic targets in BRAF mutation type colorectal cancer.