Negative BRCA1 immunohistochemistry and/or reduced RNA expression in ovarian tumors predicts germline BRCA1 mutation status. A. De Luca^{1,2 *}, J.Z. Press^{3 *}, S. Young^2,6, Y. Ridge⁶, S. Kalloger⁵, D.M. Miller⁴, D. Horsman^2,6, C.B. Gilks^2,5, D.G. Huntsman^1,2,5,6. 1) Center for Translational and Applied Genomics, Provincial Health Services Authority & BC Cancer Agency, Vancouver, BC, Canada; 2) Departments of Pathology and Laboratory Medicine; 3) Obstetrics and Gynaecology; 4) Gynecologic Oncology, University of British Columbia, Vancouver, BC, Canada; 5) Genetic Pathology Evaluation Centre of the Prostate Centre, Vancouver General Hospital, Vancouver, BC, Canada; 6) Hereditary Cancer Program, BC Cancer Agency, Vancouver, BC, Canada.
   Germline DNA from 49 consecutive women with ovarian cancer was assessed by dHPLC for BRCA1 mutations, and abnormal peaks were sequenced. BRCA1 RNA expression and loss of BRCA1 protein were assessed by real-time PCR and immunohistochemistry (IHC) [anti-BRCA1 (Ab-1), mouse mAb (MS110)], respectively. Mutation screening revealed 8/49 (16%) germline truncating BRCA1 mutations and 1 somatic BRCA1 mutation. 26/49 (53%) tumors had reduced BRCA1 RNA expression, 23/49 (47%) showed loss of BRCA1 immunoreactivity, and 19/49 (39%) had both. All cases with loss of BRCA1 immunoreactivity were high grade serous or undifferentiated. Frequency of BRCA1 germline mutations was 7/26 (27%) in patients with reduced BRCA1 tumor RNA expression and 8/23 (35%) in patients with negative BRCA1 immunoreactivity. The sole case with a somatic truncating BRCA1 mutation had loss BRCA1 expression at a protein and RNA level. 10/14 of the cancers with loss of BRCA1 immunoreactivity and no mutation had BRCA1 promoter methylation, as detected by methylation-specific PCR after bisulfite treatment. None of the 26 ovarian cancer patients with detectable BRCA1 immunostaining had a BRCA1 germline mutation. The sensitivity and specificity for detection of patients who harbour BRCA1 germline mutations were 7/8 (87%) and 22/41 (54%) for RNA expression, 8/8 (100%) and 26/41 (63%) for IHC. Ovarian carcinomas from BRCA1 germline mutation carriers had loss of BRCA protein expression. BRCA1 IHC in primary ovarian carcinoma specimens could be used to triage women for genetic counseling then BRCA1 mutation testing. *Authors contributed equally to this work.