Abstract 2487: Functional characterization of the BRCA2 variant, K3326X

Individuals with germline mutations in the breast cancer susceptibility gene, BRCA2, have an approximate 70% risk of developing breast cancer, a 30% risk of developing ovarian cancer, a 20-fold increased risk of developing prostate cancer, and a 10-fold risk of developing pancreatic cancer during their lifetime. Loss of function germline mutations in BRCA2 affect its role in the homologous recombination (HR) DNA repair pathway leading to significant genomic instability. In addition to deleterious truncating mutations, several sequence variants, collectively called Variants of Unknown Significance (VUS), have been identified and are distributed along its length. One such variant is rs11571833, a nonsense mutation in the last exon (c.9976A>T, K3326X), resulting in the loss of the C-terminal 93 amino acid residues in BRCA2. This truncated variant has been previously described as a polymorphism that does not increase susceptibility to breast and ovarian cancers, and as a neutral unclassified variant non-deleterious to its function. However, recent studies identified K3326X to be enriched in breast cancer cases and to increase the risk for lung, pancreatic, ovarian, and upper aero-digestive tract cancers. Preliminary data, obtained from the Rutgers Cancer Institute of New Jersey breast cancer case-control study, identified K3326X enrichment in 1.25% of cases compared to 0.7% of controls. Several of the carriers had second primaries and displayed a trend toward increased number of family members diagnosed with colon cancer. Notably, K3326X was also identified in 1.38% (11 of 796) of our histologically-diverse cohort of genomically-profiled tumors that included cancers of the breast, ovarian/fallopian tube, lung, vulvar, cancer of unknown primary, and one breast cancer case having prolonged response to platinum-based therapy. Thus, K3326X may represent a functional loss of wild type BRCA2 function, as we observe concomitant loss of heterozygosity at this locus. In a preliminary study, we evaluated the K3326X variant, in vitro, in a functional DR-GFP-based reporter assay measuring HR. Our data reveal the BRCA2 K3326X variant to be impaired in the HR pathway indicating a loss of wild-type protein function. We will also evaluate cell viability of the K3326X variant in the presence of DNA damaging drugs like cisplatin, poly-ADP ribose polymerase inhibitors and mitomycin C. Future studies will also incorporate a retrospective evaluation of tumor specimens that have undergone comprehensive genomic profiling. These data would indicate that BRCA2 K3326X represents a functional hypomorphic variant that may have implications in therapeutic approaches and cancer risk evaluations across a spectrum of tumor types. Citation Format: Srilatha R. Simhadri, Sonia C. Dolfi, Atul Kulkarni, Bing Xia, Shridar Ganesan, Kim M. Hirshfield. Functional characterization of the BRCA2 variant, K3326X [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 2487. doi:10.1158/1538-7445.AM2017-2487