Negative reactions of BRAF mutation-specific immunohistochemistry to non-V600E mutations of BRAF.

BRAF mutations are rare driver mutations in non-small cell lung cancer (NSCLC), accounting for 1%-2% of the driver mutations, and the mutation spectrum has a wide range in contrast to other tumors. While V600E is a dominant mutation in melanoma, more than half of the mutations in NSCLCs are non-V600E. However, treatment with dabrafenib plus trametinib targets the BRAF V600E mutation exclusively. Therefore, distinguishing between V600E and non-V600E mutations is crucial for biomarker testing in NSCLC in order to determine treatment of choice. Immunohistochemistry (IHC) using the BRAF V600E mutation-specific antibody is clinically used in melanoma patients, but little is known about its application in NSCLC, particularly with regard to the assay performance for non-V600E mutations. In the present study, we examined 117 tumors with BRAF mutations, including 30 with non-V600E mutations, using BRAF mutation-specific IHC. None of the tumors with non-V600E mutations, including two compound mutations, showed a positive reaction. Furthermore, all V600E mutations were positive except for one case with combined BRAF V600E and K601_W604 deletion. Our findings confirmed that the BRAF V600E mutation-specific IHC is specific without any cross-reactions to non-V600E mutations, suggesting that this assay can be a useful screening tool in clinical practice.