Abstract 2344: Cardiometabolic health and risk of breast cancer subtypes among US Black women.

Abstract Background: In the United States (US), Black women are more likely to be diagnosed with estrogen receptor (ER)-negative breast cancers as compared with White women. Cardiometabolic conditions are also more common among Black women. Understanding their associations with risk of breast cancer subtypes may help to explain racial differences in breast cancer risk. Prior studies have identified obesity as a risk factor for postmenopausal ER+ breast cancer and type 2 diabetes as a probable risk factor for ER- breast cancer. The goal of the present study was to comprehensively evaluate the associations of cardiometabolic factors with breast cancer subtypes in a large population of US Black women. Methods: The Black Women's Health Study is a prospective study of 59,000 self-identified US Black women. Cardiometabolic factors that have been queried every two years since the start of the study in 1995 include high body mass index (BMI ≥30 kg/m2), type 2 diabetes, hypertension, and hypercholesterolemia. Breast cancer cases were identified through self-report on biennial questionnaires, review of death certificates, and linkage to cancer registries. Hospital or registry-recorded pathology data were used to classify cases by ER status and to assign breast cancer subtypes (luminal A-like, luminal B-like, HER2-overexpressed, and triple negative). We used competing risk Cox proportional hazards models to estimate the associations between cardiometabolic factors and breast cancer subtypes, adjusting for age, reproductive factors, and lifestyle factors. Results: In comparisons of women with each cardiometabolic exposure to those without that exposure, elevated BMI was associated with an increased risk of luminal A-like breast cancer among postmenopausal women (hazard ratio [HR] 1.32 (1.03-1.68) for BMI ≥30 kg/m2 versus <25 kg/m2). All other results were not statistically significant. When we repeated the analyses using a common referent group (those with no cardiometabolic conditions), no patterns of association were observed among premenopausal women. Among postmenopausal women, HRs for all cardiometabolic factors were above 1.00 for ER+ breast cancers, although none of the HRs were statistically significant. In analyses of combined groups of cardiometabolic factors, the HR for three or more cardiometabolic conditions versus none was 1.32 (0.98-1.77) for ER+ breast cancer in postmenopausal women. Conclusions: In this large study of US Black women, poorer cardiometabolic health was associated with a higher risk of postmenopausal ER+ breast cancer. The observed association seems to be driven by the positive association of obesity with postmenopausal luminal A-like breast cancer, as has been seen in other racial and ethnic groups. Citation Format: Yifei Shan, Sarah M. Rothbard, Lynn Rosenberg, Julie R. Palmer, Mollie E. Barnard, . Cardiometabolic health and risk of breast cancer subtypes among US Black women [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2344.