Assessment of BRAF V600E Mutation Status by Immunohistochemistry in Lung and Ovarian Carcinomas
Oluyomi E Kabiawu-Ajise, Julie T Feldstein, Robert Soslow, Douglas Levine, Marc Ladanyi, Maria E Arcila. Memorial Sloan-Kettering Cancer Center, New York, NY
Background: BRAF mutations are implicated in the pathogenesis of several cancers, including melanoma, lung adenocarcinoma (ADC), colorectal cancer (CA), thyroid CA, ovarian CA and hairy cell leukemia. The V600E mutation is the most common and is emerging as an important biomarker of prognostic and therapeutic significance. While the BRAF mutation status is most commonly determined by DNA-based methods, the use of immunohistochemistry with a mutation-specific antibody has been recently described in thyroid CA, melanoma and hairy cell leukemias as a highly reliable and cost effective method of screening. Its application in lung ADC and ovarian CA, where the V600E mutation is less frequent, (∼2% and 11%, respectively), is not well described.
Design: We evaluated the performance of the BRAF V600E mutation-specific antibody (clone VE1) in molecularly characterized ovarian serous carcinomas and lung adenocarcinomas. Paraffin embedded tissue blocks were obtained from 154 surgically resected lung adenocarcinomas and 67ovarian serous carcinomas. Tumor samples were prepared in tissue microarrays and stained by immunohistochemistry with the BRAF V600E mutation-specific antibody, clone VE1. Whole tissue sections were analyzed in 16 cases. The pattern of expression was graded based on intensity of cytoplasmic staining in a 0 to 3+ scale and results were correlated with the mutation status as determined by standard DNA-based molecular methods.
Results: A total of 18 BRAF V600E mutated cases had been identified by molecular testing (10 lung, 8 ovary). The staining intensity in BRAF V600E mutated tumor samples ranged from weak (1+) to strong (3+). In lung adenocarcinomas, IHC with the VE1 antibody showed a sensitivity of 60% and a specificity and positive predictive value of 100% using a positivity cut off of 2+. In ovarian tumors, the sensitivity reached 88% with specificity and PPV of 100%. Non-specific, weak and diffuse cytoplasmic staining was identified in 85% and 89% of lung and ovarian cases, respectively, precluding the use of a 1+ cytoplasmic staining cutoff for positivity. Non-specific nuclear staining was also identified in some cases.
Conclusions: Immunohistochemistry using the VE1antibody to BRAF V600E could be used to establish the BRAF mutation status in ovarian and lung carcinomas. However, compared to other malignancies, the sensitivity is lowered by the non specific cytoplasmic staining imparted by mucinous or serous components within these tumors, and therefore negative staining results would not eliminate the need for BRAF mutation analysis, if clinically indicated.
Monday, March 4, 2013 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 309, Monday Morning