Classification of BRAF mutated colorectal cancer based on microsatellite stability.

553Background: BRAF mutated metastastic colorectal cancer (CRC) shows poor outcome in spite of development of the treatment. Thus, classification of BRAF mutated CRC based on therapeutic target is warranted. Particularly, about half of the BRAF mutated CRC reveals high microsatellite instability (MSI-H) that is characterized by high mutation burden and frequent infiltration of lymphocytes. Hence, the patients with BRAF mutation carrying MSI-H would potentially benefit from immune-check point inhibitor. However, the precise evaluation of immune status of these patients has not been clarified. Furthermore, the character of BRAF mutation with microsatellite stability (MSS) is not fully investigated. Methods: Transcriptomic information of BRAF mutated CRC with MSS/MSI-H was downloaded from open database, Gene Expression Omnibus (GEO); GSE75316 (n = 59), GSE35896 (n = 62), GSE39582 (n = 585). Gene expression of BRAF mutation with MSI-H/MSS (GSE75316: n = 5/3, GSE35896: n = 1/5, GSE39582: n = 31/14) were normal...