Abstract B065: Percent mammographic density and breast cancer risk among U.S. Black women
Authors: Holder Etienne X. , Bigham Zahna , Nelson Kerrie P. , Palmer Julie R. , Bertrand Kimberly A. 
Published: December 2023

Abstract
Background: High mammographic density is a well-established risk factor for breast cancer. A few studies have suggested a difference in mammographic density by race wherein Black women – who have a high risk of aggressive breast cancer subtypes – are more likely to have dense breasts compared to women of other racial/ethnic groups. It is unknown whether mammographic density may contribute to differences in breast cancer risk by tumor hormone subtype across race and ethnicity. Methods: We used a case-cohort study design to examine the association between percent mammographic density (PMD) and breast cancer risk among Black women in the United States using data from the Black Women’s Health Study (BWHS). Our study consisted of 5,904 women with digital screening (i.e., pre-diagnostic) mammograms of which 363 (6.15%) were women with breast cancer (cases) and 5,541 (93.85%) were women without breast cancer (non-cases). We used Cumulus to assess PMD. Quartiles for PMD were determined based on the distribution in the non-cases. We used logistic regression, adjusted for age and body mass index (BMI) at mammography, to estimate relative risks (RRs) and 95% confidence intervals (CIs) for the association of PMD with breast cancer overall and by estrogen receptor (ER) status. Fully adjusted models additionally included other established breast cancer risk factors. We also stratified analyses by age at mammography (&lt;55 vs. ≥ 55 years). Results: The mean age at mammography was 56 years for both cases and non-cases and approximately 70% of participants were postmenopausal. Cases had a lower mean BMI at age 18 years (20.9 kg/m2) compared to non-cases (21.4 kg/m2), while there was no difference in mean BMI at mammography between cases and non-cases. As expected, cases were more likely than non-cases to have a family history of breast cancer (25% vs. 19%). Additionally, cases had a higher mean PMD than did non-cases (26.3% vs. 24.5%). Overall, women in the highest quartile of PMD had a 58% higher risk of breast cancer compared to those in the lowest quartile (RRQ4vsQ1 1.58; 95% CI: 1.14, 2.18). Corresponding RRs were 1.46 (95% CI: 0.99, 2.14) for ER+ cancer and 1.57 (95% CI: 0.79, 3.14) for ER– cancer. Among women under 55 years of age, the RR for the highest quartile of PMD relative to the lowest quartile was 1.35, 95% CI: 0.83, 2.19). Among the older women, the comparable RR was 1.75, 95% CI: 1.13, 2.69). Associations were largely unchanged in multivariable models. Conclusion: In the largest study of mammographic density in U.S. Black women to date, we confirmed that higher PMD is associated with both ER+ and ER– breast cancer risk in this population. Associations were statistically significant among women ≥55 years of age. Findings from this study reinforce the importance of breast density as a risk factor for breast cancer across racial/ethnic groups.
Citation Format: Etienne X. Holder, Zahna Bigham, Kerrie P. Nelson, Julie R. Palmer, Kimberly A. Bertrand. Percent mammographic density and breast cancer risk among U.S. Black women [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr B065.