Immunohistochemical (IHC) Detection of Mutated BrafV600E along the Spectrum of Thyroid Carcinoma (TC) Progression
Ronald Ghossein, Julio Ricarte-Filho, Jeffrey Knauf, Michael Rivera, James Fagin. Memorial Sloan-Kettering Cancer Center, New York, NY
Background: Recently, the mutated BRAFV600E protein has been specifically detected in papillary thyroid carcinoma (PTC) using IHC. (Am J Surg Pathol 36: 844, 2012). Questions have also been raised about whether BRAFV600E is a clonal or subclonal event in TC. Our aims were to 1) compare BRAF V600E IHC expression in PTC, poorly differentiated (PDTC) and anaplastic TC (ATC) with mutation analysis 2) study the distribution of BRAF V600E expression within TC 3) correlate the IHC findings with the cytologic phenotype of PDTC.
Design: Whole sections and tissue microarray from 31 PTC, 38 PDTC and 22 ATC were subjected to both mass spectrometry genotyping for BRAFV600E mutation as well as IHC using the antibody VE1 directed against the V600E BRAF protein. Staining intensity was scored as 0 (no staining), 1+ (faint), 2+ (moderate) and 3+ (strong). Homogeneous expression was defined as analogous labeling intensity in > 80% of the tumor cells.
Results: 15 of 31 (48%) PTC showed strong (3+) IHC staining and BRAFV600E mutation while the remaining 16 (52%) showed 0/1+ staining and no BRAF mutations. 33 of the 38 (87%) PDTC showed0/1+ staining and no BRAF mutations while 5 (13%) contained BRAF mutations with a staining intensity of 2+ (2 cases) and 3+ (3 samples). All 12 PDTC with an exclusively follicular/Hurthle phenotype lacked BRAF mutations and showed 0/1+ staining. 5 of the 24 (21%) PDTC with PTC phenotype harbored BRAF mutations with a 2+/3+ IHC labeling. All 14 ATC with a staining intensity of 3+ harbored BRAF V600E mutations while the 2 ATC with 0/1+ staining lacked BRAF mutations. Six ATC showed a staining of 2+ including 5 with a high background staining. Of those 6 cases, BRAFV600E mutation was present only in the tumor without background. In all 10 ATC with associated PTC, both components of the tumor showed BRAFV600E mutation and strong expression. Homogeneous staining was found in 15 of 16 classical PTC (94%), 34 of 35 (97%) PDTC and 18 of 21 ATC (86%).
Conclusions: 1) Absent/faint staining for the VE1 antibody correlates perfectly with lack of BRAFV600E mutation while strong staining is always synonymous of BRAFV600E mutation in PTC, PDTC and ATC. Moderate staining intensity cannot be relied upon and should lead to genotypic analysis. 2) BRAFV600E expression correlates with PDTC and ATC derived from PTC. 3) Homogenous staining occurs in the vast majority of cases indicating that BRAFV600E mutation is a clonal event in TC.
Monday, March 4, 2013 1:00 PM
Proffered Papers: Section H, Monday Afternoon