Background:: Breast cancer mortality is substantially higher in Black compared to White women due in part to higher rates of poor prognosis triple-negative breast cancer (TNBC) in Black women. The influence of African ancestry on this disparity has not been adequately examined.
Methods:: Using the Women’s Health Initiative cohort of 161,808 postmenopausal women, we examined risk of TNBC in 6,166 Black participants with information on African ancestry, of whom 374 had incident localized breast cancers. African ancestry was based on genetic information from 656,852 single nucleotide polymorphisms with ancestry groups stratified by <80% vs ≥80% African ancestry (median split).
Results:: Breast cancer incidence, including TNBC incidence, deaths from breast cancer, and deaths after breast cancer did not differ by percentage African ancestry, however, higher mortality rates were seen after 10 years follow-up in those with ≥80% African ancestry.
Conclusion:: Percentage African ancestry alone is not significantly associated with TNBC among US Black postmenopausal women. Increased mortality rates 10 years following diagnosis seen in those with ≥80% African ancestry may be associated with the adverse influence on subsequent cardiovascular disease.
Impact:: The contribution of cardiovascular disease to the disparity in breast cancer mortality in US Black women requires further study.