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.