[2049] BRAF Mutations in Metastatic Malignant Melanoma: Comparison of Molecular Analysis and Immunohistochemical Expression

Laleh Ehsani, Cynthia Cohen, Kevin E Fisher, Momin T Siddiqui. Emory University Hospital, Atlanta, GA

Background: Melanoma is a complex genetic disease, and multiple genetic alterations have been reported to play a role during disease progression. The dysregulation of BRAF signaling has been shown to affect many molecules that promote the continual progression of melanoma. Oncogenic BRAF expression plays a vital role in promoting cell invasion and metastasis in melanoma. It is also associated with poor prognosis in metastatic melanoma. 40% to 60% of cutaneous melanomas have BRAF mutations and about 90% of the mutations involve a specific substitution at codon 600 (BRAF V600E). In this study, we compared BRAF (V600 E) mutation detection by molecular analysis with BRAF expression by immunohistochemistry (IHC).
Design: We selected 25 cases of metastatic malignant melanoma, 19 excisional biopsies and 6 fine needle aspiration cell blocks (CB). BRAF V600 E mutations were detected using the COBAS® 4800 BRAF V600 Real-time PCR assay and IHC expression with the Dako Autostainer, the BRAF V600 EP152Y monoclonal antibody (Abcam, 1:20), and high pH antigen retrieval (Trilogy, Cell Marque). IHC results were interpreted as positive if more than 10% of melanoma cells showed cytoplasmic staining of 2+ or 3+ intensity. Three pancreatic lesions were immunostained as negative controls. Molecular analysis was used as the gold standard for statistical analysis.
Results: 10/25 (40%) cases were positive by molecular analysis and 17/25 (68%) cases by IHC. All positive cases by molecular analysis were positive by IHC (100%). All 3 (100%) negative controls were negative.

Statistical analysis of BRAF V600 mutation by molecular analysis and IHC

Conclusions: Molecular testing for the BRAF V600 E mutation in metastatic malignant melanoma remains the more accurate and sensitive methodology. IHC yields a very high sensitivity but, due to increased false positivity, the specificity is much lower which may be due to the presence of other BRAF point mutations. However, IHC testing is less expensive and widely available to most laboratories when compared to molecular analysis. Hence, it can be useful for initial screening evaluation of BRAF mutations in metastatic malignant melanoma. Molecular testing can be supplemental for IHC positive or equivocal cases, as a confirmatory test resulting in considerable cost containment.
Category: Techniques

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 304, Monday Morning


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