Abstract B065: Percent mammographic density and breast cancer risk among U.S. Black women

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 (