BRAF V600E protein detection by immunohistochemistry in metastatic colorectal cancer tissue: association with tumor characteristics and <i>KRAS</i> mutation

Immunohistochemistry (IHC) using the BRAF V600E antibody is a sensitive and specific method for detecting BRAF V600E mutations in colorectal cancer (CRC). Given that BRAF and KRAS mutations are mutually exclusive, this study aimed to assess the expression of BRAF V600E in CRC according to KRAS mutation status. Automated IHC analysis was performed on tissue samples from metastatic CRC patients diagnosed between 2012 and 2022 using the anti-BRAF V600E antibody (GenomeME, IHC600). Positive and negative control tissues were used for validation. Cytoplasmic staining was considered positive, with intensity classified as weak, moderate, or strong. The percentage of positive tumor cells was recorded semi-quantitatively. Thirty-five cases were included.The mean age of patients was 60 years (±12.41), with a male-to-female ratio of 2.9. KRAS mutations were present in 48% of cases. BRAF V600E cytoplasmic staining was observed in 37.1%, with a mean percentage of positive cells of 50% (range: 5%-100%). Diffuse and focal staining were found in 7/13 and 6/13 cases, respectively. Significant associations were observed with mucinous carcinoma subtype, invasion patterns, and lymph node metastasis. All KRAS-mutated cases showed negative BRAF staining. Complete absence of BRAF V600E IHC staining in CRC is strongly associated with KRAS mutation, suggesting IHC as an efficient tool to predict KRAS mutational status.