Club de Revistas de Dermatopatología. Jueves 4 de abril 2013

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Immunohistochemistry is highly sensitive and specific for the detection of V600E BRAF mutation in melanoma.

Long GV, Wilmott JS, Capper D, Preusser M, Zhang YE, Thompson JF, Kefford RF, von Deimling A, Scolyer RA. Am J Surg Pathol. 2013 Jan;37(1):61-5. doi: 10.1097/PAS.0b013e31826485c0.

PubMed  https://www.ncbi.nlm.nih.gov/pubmed/23026937?dopt=Abstract

This study investigated the sensitivity and specificity of immunohistochemical (IHC) analysis using an anti-BRAF antibody to detect the presence of the BRAF V600E mutation in patients with metastatic melanoma. A total of 100 patients with American Joint Committee on Cancer stage IIIC unresectable or stage IV melanoma and who underwent tumor DNA BRAF mutation testing were selected. Paraffin-embedded, formalin-fixed melanoma biopsies were analyzed for the BRAF mutation status by independent, blinded observers using both conventional DNA molecular techniques and IHC with the novel BRAF V600E mutant-specific antibody, VE1. The antibody had a sensitivity of 97% (37/38) and a specificity of 98% (58/59) for detecting the presence of a BRAF V600E mutation. Of the BRAF-mutated cases, none of the non-V600E cases (including V600K) stained positive with the antibody (0/11). There were 5 cases with discordant BRAF mutation results. Additional molecular analysis confirmed the immunohistochemically obtained BRAF result in 3 cases, suggesting that the initial molecular testing results were incorrect. Two of these patients would not have received a BRAF inhibitor on the basis of the initial false-negative mutation testing result. Two cases remained discordant. The reported IHC method is an accurate, rapid, and cost-effective method for detecting V600E BRAF mutations in melanoma patients. Clinical use of the V600E BRAF antibody should be a valuable supplement to conventional mutation testing and allow V600E mutant metastatic melanoma patients to be triaged rapidly into appropriate treatment pathways.

Immunohistochemical analysis of BRAF(V600E) expression of primary and metastatic melanoma and comparison with mutation status and melanocyte differentiation antigens of metastatic lesions.

Busam KJ, Hedvat C, Pulitzer M, von Deimling A, Jungbluth AA. Am J Surg Pathol. 2013 Mar;37(3):413-20. doi: 10.1097/PAS.0b013e318271249e.

PubMed  https://www.ncbi.nlm.nih.gov/pubmed/23211290?dopt=Abstract

BRAF(V600E) is the most common mutation in cutaneous melanoma and has become the target of treatment for patients with metastatic melanoma. A number of methods are currently available to determine mutation status. Recently, a monoclonal antibody (VE1) against mutant BRAF(V600E) was generated. Its use permits assessment of the mutant protein expression throughout a tumor sample and may allow faster and cheaper determination of the mutation status in selected cases. However, for BRAF(V600E) protein expression analysis to be of clinical value, high sensitivity and specificity of the antibody is a prerequisite. In this study we analyzed 44 metastatic melanoma samples with a known BRAF(V600E) mutation status with immunohistochemical expression of the BRAF(V600E) protein. None of the 22 tumors that lacked the BRAF(V600E) mutation labeled with the antibody VE1. This set of VE1-immunonegative tumors included 4 metastatic lesions with the BRAF(V600E) mutation. All 22 tumor samples that were known to carry the BRAF mutation were immunoreactive with VE1. Sixteen of them stained strongly and homogenously throughout the tumor sample. However, 6 tumor samples contained both BRAF(V600E)-immunopositive and BRAF(V600E)-immunonegative cell populations. When the BRAF status was compared with immunoreactivity for melanocyte differentiation antigens, no significant difference in the expression of melan-A, microphthalmia transcription factor, gp100, or tyrosinase was found between mutant and wild-type tumors. In addition to metastatic lesions, we also examined 20 primary melanomas for the expression of BRAF(V600E). Seven of 10 superficial spreading melanomas were immunoreactive with the antibody VE1. Five tumors were strongly and homogenously immunoreactive. In 2 primary tumors the staining was focal, involving only a subpopulation of the tumor. None of the nonsuperficial spreading melanomas was immunoreactive. In 7 primary tumors the mutation status could be analyzed: only tumors carrying the BRAF(V600E) mutation were immunoreactive with VE1. The high specificity and sensitivity of VE1 for the detection of mutant BRAF(V600E) suggests a valuable reagent for clinical purposes. Heterogeneity in BRAF expression may be relevant for treatment response to BRAF inhibitors.

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