LAUSR

e13127 Background: Approximately, 10% of breast cancer (BC) are related to inherited germline mutations. BRCA1/2, the most recognized and tested genes, are responsible for 50% of hereditary BC. Genetic testing for hereditary BC has changed significantly. Increasing evidence suggests parallel multigene testing. Methods: NGS-based germline BRCA status assessment was performed on 209 high risk BC patients with at least one of the following risk factors: triple negative BC, early onset ( < -45), with a family history of BC, bilateral BC and male BC. Multigene-panel testing was subsequently offered to patients with at least 2 of the risk factors and WT germline BRCA. Capture-base targeted sequencing was performed on white blood cells using a panel consisting of 53 hereditary cancer-related genes, spanning 229kb of human genome. Results: Among the 209 patients screened, only 12 patients had pathogenic BRCA1/2 mutation. Next, we investigated the prevalence of non- BRCA pathogenic germline pathogenic mutations in patients with at least 2 risk factors. Thirty-seven patients met the criteria and only 23 patients had sufficient WBC DNA for sequencing. This cohort had a median age of 42, with a majority carrying infiltrating ductal carcinoma. Except for one bilateral BC patient who had stage IV disease, all other patients had early stage disease. We identified 5 pathogenic mutations from 5 patients spanning 4 genes: PALB2, PTEN, ATM and WRN, resulting in a prevalence rate of 20% for pathogenic germline mutations in high risk germline BRCA WT BC patients. Two patients carried mutations in PALB2, one with a frameshift and another with a splice mutation. Mutation types for PTEN, ATM and WRN were splice mutation, stop gain mutation and frameshift mutation, respectively. All 5 patients were diagnosed with BC before the age of 40. Three of them had bilateral BC; one had triple negative BC and another patient had a family history of BC. Conclusions: Our study confirms the clinical significance of testing non- BRCA genes, and suggests multigene panel testing for patients at risk for hereditary BC. Such approach increases the identification of hereditary BC, thus impacting clinical decision-making.