BRAF V600E Mutations in Thyroid Carcinomas: Is There a Role for BRAF Immunohistochemistry?
Kevin E Fisher, Laleh Ehsani, Stewart G Neill, Shelley A Caltharp, Momin T Siddiqui, Cynthia Cohen. Emory University School of Medicine, Atlanta, GA
Background: BRAF V600E mutations promote tumorigenesis via constitutive activation of the mitogen activated protein kinase pathway leading to dysregulated cellular proliferation and increased survival. BRAF V600E (T→A 1799) point mutations are seen in approximately 45% of papillary thyroid carcinomas (PTCs) and current practice algorithms endorse molecular testing for most patients with a diagnosis of PTC. In this study, we examined the utility of immunohistochemical (IHC) BRAF overexpression to identify thyroid carcinomas harboring BRAF V600E mutations.
Design: We selected a total of 41 cases for analysis: 31 papillary, 1 follicular (FTC), 5 medullary (MTC), and 4 anaplastic (ATC) thyroid carcinomas from 37 thyroidectomies and 4 fine needle aspiration cell blocks. IHC was performed with the Dako Autostainer, the BRAF EP152Y monoclonal antibody (MAB, Abcam, 1:20 dilution), and high pH antigen retrieval (Trilogy, Cell Marque). Tumors were considered to overexpress BRAF if greater than 10% of neoplastic cells showed 2+ or 3+ cytoplasmic staining. Baseline expression was determined using three pancreatic tumors. BRAF mutations were confirmed using pyrosequencing. Molecular analysis was used as the gold standard for statistical analysis.
Results: 33/41 (80%) of carcinomas overexpressed BRAF by IHC (27 PTCs, 1 FTC, 3 MTCs, and 2 ATCs). 12 PTCs (39%) and 2 ATCs (50%) harbored BRAF V600E mutations; all overexpressed BRAF by IHC. No BRAF V600E mutations were detected in the FTC or 5 MTCs. All 8 carcinomas that did not demonstrate BRAF overexpression were BRAF V600E negative (sensitivity 100%, NPV 100%). 19 tumors (46%) overexpressed BRAF by IHC but were BRAF V600E negative (specificity 29.6%, PPV 42.4%).
|BRAF IHC + / V600E +||BRAF IHC + / V600E -||BRAF IHC - / V600E +||BRAF IHC - / V600E -|
|Total (n=41)||14 (34%)||19 (46%)||0 (0%)||8 (19%)|