Familial breast/ovarian cancer and BRCA1/2 genetic screening: the role of immunohistochemistry as an additional method in the selection of patients

Abstract

Only 20-25% of families screened for BRCA1/2 mutations are found positive. Because only a positive result is informative, we studied the role of BRCA1/2 immunohistochemistry as an additional method for patient selection. From 53 high-risk-affected probands, 18 (34%) had available paraffin blocks of their tumors and were selected for this study. Mutation screening was done by conformation-sensitive gel electrophoresis and multiplex ligation-dependent probe amplification. For immunohistochemistry, 21 neoplastic specimens (15 breast carcinomas, 5 ovary neoplasms, and 1 rectal adenocarcinoma) were analyzed with BRCA1 (monoclonal antibody, Ab-1, oncogene) and BRCA2 (polyclonal antibody, Ab-2, oncogene) antibodies. Absence of the BRCA1 protein was confirmed in negative tumors by Western blotting. Seven patients were positive for BRCA1/2 mutations: 5 for BRCA1 and 2 for BRCA2. Four out of five positive patients had tumors negative for BRCA1 immunostaining, and the remaining 13 BRCA1-negative patients had positive BRCA1 immunostaining in all tumor samples. Sensitivity to predict for BRCA1 mutation carriers was 80%, and specificity was 100%, with a positive predictive value of 100% and a negative predictive value of 93%. This correlation was statistically significant (p=0.001). No correlation was observed for BRCA2. If larger studies confirm these results, high-risk patients with BRCA1-negative tumors should be screened first for this gene.

Figure 1

BRCA1 immunohistochemistry in cancer specimens. (A) Breast cancer specimen with clear nuclear BRCA1 labeling in cancer (bcc), epithelial (ebc), and stromal (sc) cells contrasts with an ovarian cancer sample (B), where cancer cells (occ) are negative for BRCA1, even if inflammatory (ic), and stromal cells (sc) keep the expected nuclear labeling.

Figure 2

Absence of BRCA1 protein in negative breast cancer specimens. After Western blotting of tumor protein extracts with the Ab-1 antibody, BRCA1 protein was identified in normal breast, positive control (1) and in breast cancer from a BRCA1 mutation-negative woman but with positive Ab-1 immunostaining (2). In BRCA1 mutation-positive cases with negative immunostaining, the 220-kDa band corresponding to the BRCA1 protein was not observed (3 and 4). Negative control, protein G-Sepharose beads with Ab-1 monoclonal antibody (5).