A better understanding of gene-specific risks for development of breast cancer will lead to improved screening, prevention, and therapeutic strategies for individuals identified to carry germline mutations. We performed targeted massively-parallel sequencing to identify mutations and large genomic rearrangements in 26 known or proposed breast cancer susceptibility genes in 2134 BRCA-negative women with familial breast cancer (FBC). A case-control analysis was performed comparing the frequency of internally classified mutations identified in FBC cases to that in non-Finnish European controls from the Exome Aggregation Consortium (ExAC) excluding samples from The Cancer Genome Atlas. Including large genomic rearrangements, mutations were identified in 8.2% of FBC cases compared to 6.2% of ExAC controls, including mutations in high-penetrance genes (0.6% in cases vs. 0.1% in controls), moderate-penetrance genes (3.7% vs 1.7%), and seven cases with two mutations (0.3%). The remainder of FBC cases and ExAC controls had mutations in proposed breast cancer genes (1.6% of cases vs 2.4% of controls), Lynch syndrome genes (0.5% vs. 0.5%) or were heterozygous MUTYH carriers (1.5% vs. 1.5%). Case-control analysis demonstrated significant associations with FBC for ATM, PALB2, and TP53 mutations (OR>3.0, p<10-4), BARD1 mutations (OR=3.2, p=0.012), and CHEK2 truncating mutations (OR=1.6, p=0.041). Our results therefore demonstrate that only approximately 4% of BRCA1/2 negative FBC patients have mutations in genes definitively associated with breast cancer at this time. Large case-control studies are needed to fully evaluate the breast cancer risks associated with moderate penetrance and proposed breast cancer susceptibility genes.

Citation Format: Kara N. Maxwell, Thomas Paul Slavin, Jenna M. Lilyquist, Joseph Vijai, Susan L. Neuhausen, Steven N. Hart, Vignesh Ravichandran, Tinu Thomas, Ann Maria, Kasmintan A. Schrader, Raymond Moore, Chunling Hu, Brad Wubbenhorst, Brandon M. Wenz, Kurt D'Andrea, Susan M. Domchek, Mark E. Robson, Paulo Peterlongo, Paolo Radice, James M. Ford, Judy E. Garber, Csilla Szabo, Kenneth Offit, Katherine L. Nathanson, Fergus J. Couch, Jeffrey N. Weitzel. Risks of familial breast cancer associated with known and proposed breast cancer susceptibility genes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4265. doi:10.1158/1538-7445.AM2017-4265