Abstract

Background: Identification of actionable mutations in melanomas is important for guiding clinical management. 40-60% of melanomas harbor mutations in B-Raf proto-oncogene (BRAF), with V600E locus mutation being most common. Although molecular methods (e.g. next-generation sequencing; NGS) are the gold standard, they are expensive and have long turn-around time. Assessing BRAF V600E mutational status with immunohistochemistry (IHC) offers a quick and cost-effective alternative. To date, no standardized scoring systems for interpreting BRAFV600E IHC in melanomas have been described. Methods: Retrospective chart review identified 63 cutaneous melanomas with concurrent NGS data between 2012-2023. Study group included cases with positive BRAF or RAS mutations (n=42). Control group included cases with negative BRAF or RAS mutations (n=21). BRAFV600E IHC was performed and interpreted by four pathologists using a 4-point system (0: negative cytoplasmic staining, 1+: <50% of cells with weak cytoplasmic staining, 2+: >50% weak-moderate cytoplasmic staining OR <50% strong cytoplasmic staining, 3+: >50% strong cytoplasmic staining). Results: Of the study group, 100% BRAF V600E mutated cases scored 2+ (3/7) or 3+ (4/7) and 100% (n=25) with BRAF non-V600E or RAS mutations scored 0 or 1+. 100% of control group scored 0 or 1+. The sensitivity and specificity of BRAFV600E IHC are both 100% with >/= 2+ as the cut-off. Conclusion: The scoring system for BRAFV600E IHC with a cutoff score of =/> 2+ is highly sensitive and specific at identifying BRAF V600E mutated melanomas. Thus, it offers an efficient option in determining an actionable mutation and for screening cases that may need further molecular analysis.