V600E BRAF Mutation in Vulvovaginal Melanoma Is Rare: A Study of Anti-Human BRAF V600E Monoclonal Antibody in 24 Cases
Maheshwari Ramineni, Anais Malpica, Raja Luthra, Michael T Deavers, Elizabeth D Euscher. University of Texas MD Anderson Cancer Center, Houston, TX
Background: BRAF mutation may be present in up to 60% of melanoma, and its detection has therapeutic significance. The gold standard detection method is DNA sequencing (DNAs), which is labor intensive. In mucosal melanoma (MM), the reported incidence of BRAF mutation from all mucosal sites is low (10-15%). This study presents the findings of BRAF mutational analysis in 24 patients (pts) with vulvovaginal melanoma (VVM) and evaluates a new antibody directed against the most common BRAF mutation, V600E, to determine whether it could be used in place of DNAs particularly in tumors with a low incidence of BRAF mutation.
Design: Twenty-four VVM (8 vulvar; 16 vaginal) melanomas had BRAF mutation analysis by a PCR-based primer extension assay screening for the following mutational hot spots: G464, G466 (bases 1 and 2), G469, D594, L597R, V600 (all 3 bases) and K601 (bases 1 and 3). All VVM were then stained with anit-human BRAF V600E monoclonal antibody using the Bond Max stainer (clone VE1; 1:50, Spring Bioscience, Pleasanton, CA). Immunohistochemistry on nonMM previously tested by DNA sequencing with (n=21) and without (n=4) a V600E BRAF mutation served as a control.
Results: 21 pts with VVM had no BRAF mutation, and 3 pts (12.5%) had detectable BRAF mutation by DNAs: V600E, 1 pt; V560 1 pt; L576, 1 pt. Staining with anti-BRAF V600E antibody was positive in the 1 pt (4%) with a V600E mutation by DNAs. There was no staining observed in the 2 pts with variant BRAF mutation. No cases of VVM negative by DNAs had staining by immunohistochemistry (IHC). 20 of 21 cases (95%) with V600E mutation detected by DNAs had staining with the V600E antibody. 1 of 4 cases of non MM with no BRAF mutation by DNAs had staining by IHC. In this case, the amount of tumor in the sample was low; the possibility of tumor amount below the limit of detection could not be excluded.
Conclusions: The incidence of BRAF mutation in VVM is low (12.5%) and within the reported range of BRAF mutation detection in MM from all sites. BRAF antibody directed against the V600E clone is sensitive (95.5%) and specific (96.3%) in this small series. The antibody does not appear to detect variant BRAF mutations. Based on the results of this small study, IHC for BRAF antibody may be a cost effective alternative to DNAs particularly in tumors with a low incidence of BRAF. Further study on a larger scale is required to determine whether BRAF IHC could be used in place of molecular testing in all cases of melanoma.
Category: Gynecologic & Obstetrics
Tuesday, March 5, 2013 9:00 AM
Proffered Papers: Section E, Tuesday Morning