The utility of BRAFV600E mutation-specific antibody for colon cancers with microsatellite instability.

This study's objective was to assess the performance of immunohistochemical staining with the BRAF mutation-specific antibody (clone VE1) in tissue from colon cancers, including those with a high degree of microsatellite instability (MSI-H). VE1 was applied to tissue microarrays of 152 colon cancers with known MSI status. Results of immunohistochemical analyses were scored as negative, positive, or equivocal. The results of VE1 immunohistochemical analysis were compared with BRAF mutation analysis by PCR. Fifteen of the 152 cases (10%) were positive with VE1 immunohistochemical analysis, 8 were equivocal, and 129 were negative. There was a single false-negative case and no false positives were identified when 74 VE1-positive or VE1-negative cases were tested by the BRAF PCR testing. Of the 8 equivocal VE1 cases identified, 3 were BRAF-positive. In the 17 MSI-H colon cancers, VE1 immunohistochemical analysis resulted in 7 true-positive, 9 true-negative, and 1 false-negative case when compared with PCR results. The sensitivity and specificity of VE1 in the MSI-H colon cancer group were determined to be 88% and 100%, respectively. The BRAF positivity rate by VE1 immunohistochemical analysis in MSI-H colon cancers is consistent with that of published cohorts, which use molecular assays, and the accuracy of positive or negative VE1 staining is high. A small subset of equivocal cases (5% in our cohort) with heterogenous staining requires confirmation by the BRAF mutation analysis. We propose a testing algorithm for Lynch syndrome screening in MSI-H colorectal cancers that incorporates VE1 immunohistochemical analysis with PCR testing for equivocal cases.