VE1 Is a Sensitive and Specific Marker for BRAF V600E Mutations in Melanoma
Ruth K Foreman, Lynette M Sholl, Justine A Barletta, Jason L Hornick. Brigham and Women's Hospital, Harvard Medical School, Boston, MA
Background: Around 50% of cutaneous melanomas harbor mutations in the BRAF gene, causing constitutive activation of the MAPK signaling pathway. The majority (90%) of BRAF mutations occur at codon 600, with a valine to glutamic acid substitution (V600E). The BRAF V600E inhibitor vemurafenib was recently approved by the Food and Drug Administration (FDA) for treatment of BRAF-mutant advanced melanoma. Sequencing is currently performed to identify BRAF mutations prior to initiating vemurafenib therapy. A monoclonal antibody VE1 directed against V600E-mutant BRAF was recently developed. The aim of this study was to validate the utility of this antibody in detection of the V600E BRAF mutation in melanoma.
Design: Whole tissue sections of 37 melanomas with known BRAF genotypes were evaluated (29 metastatic, 8 primary). 17 melanomas had BRAF V600E mutations and 20 were BRAF wild-type. 14 BRAF wild-type melanomas also had known NRAS genotype (3 with codon 61 substitutions and 11 wild-type). One additional BRAF wild-type melanoma had a known KIT mutation (at codon 822). Immunohistochemistry (IHC) was performed following pressure cooker antigen retrieval using the VE1 mouse monoclonal antibody (Spring Bioscience; 1:50 dilution). Cytoplasmic staining was scored as positive or negative; intensity was graded as weak, moderate, or strong.
Results: 15 BRAF V600E-mutant melanomas showed either diffuse strong (13; 76%) or moderate (2; 12%) cytoplasmic staining for VE1 (overall sensitivity 88%). 2 BRAF-mutant melanomas showed negative staining for VE1. 2 BRAF wild-type melanomas showed weak, non-specific nuclear staining and were scored negative. All other BRAF wild-type melanomas were completely negative for VE1 (specificity 100%).
Conclusions: VE1 is a highly sensitive and specific marker for detecting BRAF V600E mutations in melanoma. IHC with VE1 may be useful for rapid identification of BRAF mutations and triage of tissue for further genetic analysis.
Tuesday, March 5, 2013 9:30 AM
Poster Session III # 39, Tuesday Morning