Abstract 6119: Association of genetic African ancestry and triple-negative breast cancer risk: Findings from the African-ancestry breast cancer genetics consortium

Abstract Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype that lacks target treatments. It has been reported that African-American women have a higher incidence of TNBC and are diagnosed at an earlier age than women of European ancestry. This disparity may be attributed to both genetic and non-genetic risk factors that are associated with the African ancestry. In this study, we investigated whether genotype-derived African ancestry might be related to an elevated risk of TNBC, with adjustments for several known genetic and non-genetic risk factors. Included in the study are self-reported Black breast cancer patients diagnosed with TNBC (n =2, 292) or estrogen receptor (ER) -positive cancer (n =7, 863) and 9, 324 controls included in the African-ancestry Breast Cancer Genetics (AABCG) Consortium. We estimated the global ancestry by Admixture and the local ancestry by FLARE, using reference of the European- and African-ancestry samples from the 1000 Genome Project. Odds ratios (OR) and 95% confidence interval (CI) per ten percent increase of the global African ancestry proportion were estimated using logistic regressions comparing TNBC with controls (case-control analyses) or with ER-positive cases (case-case analyses), adjusted for age. Similar analyses were conducted for the local African ancestry proportion at each of the 12 genomic regions that were identified in AABCG in relation to TNBC risk. Results for each participating study were meta-analyzed using fixed or random effect models. We further adjusted for non-genetic risk factors including body mass index (BMI), number of live births, breastfeeding, and menopausal status. A polygenic risk score (PRS) was constructed using 13 independent risk variants at the 12 TNBC risk loci. The PRS was additionally adjusted to investigate whether these risk variants mediated the association of African ancestry with TNBC risk. No significant association was observed between TNBC risk and global African ancestry proportion (OR: 1. 03, 95% CI: 0. 98-1. 08) in case-control comparisons. Compared with ER-positive cases, however, TNBC cases had a higher global African ancestry, resulted in an OR of 1. 09 (95% CI: 1. 04, 1. 13, P =5. 35×10-5). A similar association was observed with additional adjustment for non-genetic risk factors, with an OR of 1. 08 (95% CI: 1. 03, 1. 12, P =0. 003). Similar patterns were also found for local ancestry proportion at six of the 12 TNBC risk loci (P 0. 05). Further adjustment for the PRS attenuated the association between global ancestry and a TNBC diagnosis in case-case comparisons (OR: 1. 05, 95% CI: 1. 01, 1. 10, P =0. 013). Our study suggests that women with a higher African ancestry are more likely to be diagnosed with a TNBC than ER-positive breast cancer and genetic factors identified to date partially explain this association. Citation Format: Guochong Jia, Lili Liu, Julie R. Palmer, Christopher A. Haiman, Wei Zheng. Association of genetic African ancestry and triple-negative breast cancer risk: Findings from the African-ancestry breast cancer genetics consortium abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6119.