Assessment of BRAF V600E (VE1) immunochemistry for the detection of BRAF V600E mutation in non–small cell lung carcinoma cytology specimens

Background: Non–small cell lung carcinoma (NSCLC) patients with BRAF V600E–mutated tumors respond to targeted therapy. Testing for BRAF V600E is commonly performed with molecular methods; however, a mutation-specific VE1 antibody clone can provide an alternative testing option using immunohistochemistry (IHC) for practices using single-gene testing and in situations when the specimen is inadequate for molecular testing. This study evaluates the usefulness of VE1 IHC in screening for BRAF V600E mutations in NSCLC cytology specimens. Methods: The authors retrospectively identified cytology cases with a diagnosis of NSCLC that had BRAF V600E IHC performed on cell block sections with the monoclonal VE1 antibody clone. The BRAF V600E IHC results were compared with those of molecular testing performed with an amplicon-based next-generation sequencing assay. Results: There were 201 NSCLC cases evaluated. The VE1 IHC was positive in seven of seven BRAF V600E–mutated tumors (100%) and was negative in 158 of 158 nonmutated BRAF V600E tumors (100%). Thirty cases did not undergo molecular testing, primarily because of insufficient tissue or because molecular testing was performed on an alternative specimen. Six cases showed equivocal weak/focal staining: Two cases demonstrated BRAF V600E mutations, and four cases were negative by molecular testing. Conclusions: This study suggests that BRAF V600E IHC can be used reliably to screen NSCLC cytology specimens, and negative results strongly indicate the absence of a BRAF V600E mutation. Having a low threshold for equivocal staining is recommended with molecular confirmation of BRAF V600E for any cases demonstrating weak and/or focal cytoplasmic staining.