LAUSR

Two recent studies have defined population-based risk of breast cancer (BC) due to pathogenic variants (PVs) in well-established BC susceptibility genes. Prior studies in high-risk BC cohorts identified variable BC risks based on the position and type of mutation in BRCA1 and BRCA2, and based on the type of mutation in ATM, CHEK2, and PALB2. Whether this variability holds true in the general population has not been evaluated. To determine the BC risks associated with mutations of different types and in different locations in BC susceptibility genes in the general population, we carried out case-control analyses of 32247 cases and 32544 controls in the CARRIERS study, including 12 US population-based studies, and case-control analyses, subset to mutation carriers. We used age-adjusted logistic regression to estimate odds ratios (OR), relative OR (rOR), and 95% confidence intervals (CI) for PVs in BRCA1, BRCA2, ATM, CHEK2, and PALB2. ORs were estimated using the full population of mutation carriers and noncarriers while rORs were estimated within subsets of individual gene mutation carriers. We identified 273 BRCA1, 421 BRCA2, 253 ATM, 351 CHEK2, and 148 PALB2 in women with BC and 35 BRCA1, 84 BRCA2, 139 ATM, 139 CHEK2, and 38 PALB2 variant carriers in those without BC. For BRCA1, we did not find differences in risk by mutation type or location. However, variants leading to nonsense mediated decay (NMD) predicted to have re-initiation at p.M128 had a non-statistical 3-fold higher risk for BC compared to those leading to NMD without re-initiation (rOR 3.1, 0.99-13.52, p = 0.0826). BRCA2 loss of function (LoF) mutations in exons 1-10 had a higher BC risk compared to LoF mutations in the exon 11 (rOR 2.7, 1.1-7.9, p=0.048) ovarian cancer cluster region (OCCR). We did not detect any differences in risk by mutation type or location in ATM, CHEK2, or PALB2. CHEK2 missense variants p.I157T (rOR 0.5, 0.4-0.7, p <0.001) and p.T476M (rOR 0.5, 0.3 - 0.8, p=0.005) were associated with lower BC risk relative to CHEK2 c.1100delC (OR 2.5, 2.0-3.3, p<0.001). The CHEK2 c.444+1G>A splicing variant was associated with highest BC risk among common CHEK2 variants (OR 4.2, 1.9-10.5, p<0.001), but was not statistically significantly different from c.1100delC (rOR 1.7, 0.8-4.3, p=0.230). In summary, we identified a higher BC risk for LoF variants in BRCA2, lower risk for CHEK2 missense mutations, and non-statistical higher risk for NMD/re-initiation BRCA1 variants and CHEK2 c.444+1G>A in this population-based study. Despite the large numbers included in the overall CARRIERS study, the number of PV carriers was relatively small, which may have limited the detection of associations. Nonetheless, we were able to detect genotype-risk associations that have implications for counseling women about their BC risk, and certainly for the development of individualized risks. Citation Format: Mwangala P. Akamandisa, Nicholas Boddicker, Chunling Hu, Siddhartha Yadav, Jeffrey N. Weitzel, Peter Kraft, Susan M. Domchek, Fergus J. Couch, Katherine L. Nathanson, for the CARRIERS Consortium . Mutation type and location in breast cancer susceptibility genes are associated with differential risk in the general population [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1183.