BRAF V600E Mutation-Specific Monoclonal Antibody Is Predictive of BRAF Mutation Status Determined by Genotyping in Papillary Thyroid Carcinoma
Cheryl A Adackapara, Brooke E Howitt, Lynette M Sholl, Jeffrey F Krane, Jason L Hornick, Justine A Barletta. Brigham and Women's Hospital, Boston, MA
Background: An activating mutation in BRAF (V600E) is identified in approximately 45% of papillary thyroid carcinomas (PTCs) and has been reported to be associated with more aggressive tumor behavior. With the advent of new targeted therapies, BRAF status is becoming increasingly important in cases of radioactive iodine refractory disease. A BRAF V600E-specific monoclonal antibody has recently become commercially available. The aim of this study was to validate this antibody in a genotyped cohort of PTCs.
Design: 44 cases of resected PTC were examined. BRAF codon 600 was genotyped in all cases using pyrosequencing. A subset of BRAF wild type (WT) cases were also tested for KRAS, NRAS and HRAS mutations using a Sequenom platform. Twenty-two tumors had BRAF V600E mutation and 22 tumors were BRAF WT (of these 6 were NRAS and 5 were HRAS mutated). Immunohistochemistry (IHC) was performed on whole sections following pressure cooker antigen retrieval with an anti-BRAF V600E monoclonal antibody (Spring Bioscience; clone VE1; 1:50 dilution with overnight incubation). Cytoplasmic staining was scored as "positive" or "negative".
Results: Cytoplasmic staining for BRAF was observed in all 22 cases with the BRAF V600E mutation. Staining was negative in all 22 cases with WT BRAF, including all cases with NRAS and HRAS mutations. Positive cases showed a homogeneous staining pattern. Negative cases frequently showed non-specific staining of tumor cell nuclei and colloid; however, this pattern was easily distinguishable from the cytoplasmic staining seen in BRAF-mutant tumors.
Conclusions: IHC for BRAF V600E is predictive of BRAF mutation status determined by genotyping in PTC. In our study the stain showed both a sensitivity and specificity of 100%.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 38, Wednesday Afternoon