[547] 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 Analysis In 41 Thyroid Carcinomas
 BRAF IHC + / V600E +BRAF IHC + / V600E -BRAF IHC - / V600E +BRAF IHC - / V600E -
PTC (n=31)121504
FTC (n=1)0100
MTC (n=5)0302
ATC (n=4)2002
Total (n=41)14 (34%)19 (46%)0 (0%)8 (19%)



Conclusions: Molecular testing for BRAF mutations in thyroid carcinomas remains the diagnostic gold standard. BRAF IHC provides excellent sensitivity and NPV, but the inability of the BRAF EP152Y MAB to discern endogenous wild-type BRAF expression from overexpressed BRAF secondary to genetic mutation (e.g. low specificity and PPV) limits the diagnostic utility of this antibody outside of an initial screening test. Additional research is needed to determine whether these results are applicable to BRAF IHC overexpression in other malignancies. Analysis with a mutation-specific BRAF V600E antibody is ongoing to improve the specificity and PPV.
Category: Endocrine

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 83, Monday Morning

 

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