Assessment of BRAF V600E Status in Colorectal Carcinoma: Tissue-Specific Discordances between Immunohistochemistry and Sequencing.

Although sequencing provides the gold standard for identifying colorectal carcinoma with BRAF V600E mutation, immunohistochemistry (IHC) with the recently developed mouse monoclonal antibody VE1 for BRAF V600E protein has shown promise as a more widely available and rapid method. However, we identified anecdotal discordance between VE1 IHC and sequencing results and therefore analyzed VE1 staining by two different IHC methods (Leica Bond and Ventana BenchMark) in whole tissue sections from 480 colorectal carcinomas (323 BRAF wild-type, 142 BRAF V600E mutation, and 15 BRAF non-V600E mutation). We also compared the results with melanomas and papillary thyroid carcinomas (PTC). With the Bond method, among 142 BRAF V600E-mutated colorectal carcinomas, 77 (54%) had diffuse VE1 staining and 48 (33%) had heterogeneous staining, but 17 (12%) were negative. Among 323 BRAF wild-type colorectal carcinomas, 196 (61%) were negative, but 127 (39%) had staining, including 7 with diffuse staining. When positivity was defined as staining in ≥ 20% of tumor cells, VE1 IHC had sensitivity of 75% and specificity of 93% for BRAF V600E mutation. With the Ventana method, among 57 BRAF V600E-mutated colorectal carcinomas, 36 (63%) had diffuse VE1 staining, whereas 6 (11%) had no or weak (<20% of tumor cells) staining. Among 33 BRAF wild-type colorectal carcinomas, 16 (48%) had no or weak staining, whereas 15 (45%) had heterogeneous staining. In contrast with colorectal carcinoma, Bond and Ventana VE1 IHC in melanoma and PTC were highly concordant with sequencing results. We conclude that VE1 IHC produces suboptimal results in colorectal carcinoma and should not be used to guide patient management.