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Background: Reduction in breast density may be a biomarker of endocrine therapy (ET) efficacy. Our objective was to assess the impact of race on ET-related changes in volumetric breast density (VBD).Methods: This retrospective cohort study assessed longitudinal changes in VBD measures in women with estrogen receptorpositive invasive breast cancer treated with ET. VBD, the ratio of fibroglandular volume (FGV) to breast volume (BV), was measured using Volpara software. Changes in measurements were evaluated using a multivariable linear mixed effects model.Results: Compared with white women (n ¼ 191), black women (n ¼ 107) had higher rates of obesity [mean AE SD body mass index (BMI) 34.5 AE 9.1 kg/m 2 vs. 30.6 AE 7.0 kg/m 2 , P < 0.001] and premenopausal status (32.7% vs. 16.7%, P ¼ 0.002). Age-and BMI-adjusted baseline FGV, BV, and VBD were similar between groups. Modeled longitudinal changes were also similar: During a follow-up of 30.7 AE 15.0 months (mean AE SD), FGV decreased over time in premenopausal women (slope ¼ À0.323 cm 3 ; SE ¼ 0.093; P ¼ 0.001), BV increased overall (slope ¼ 2.475 cm 3 ; SE ¼ 0.483; P < 0.0001), and VBD decreased (premenopausal slope ¼ À0.063%, SE ¼ 0.011; postmenopausal slope ¼ À0.016%, SE ¼ 0.004; P < 0.0001). Race was not significantly associated with these longitudinal changes, nor did race modify the effect of time on these changes. Higher BMI was associated with lower baseline VBD (P < 0.0001). Among premenopausal women, VBD declined more steeply for women with lower BMI (time  BMI, P ¼ 0.0098).Conclusions: Race does not appear to impact ET-related longitudinal changes in VBD.Impact: Racial disparities in estrogen receptor-positive breast cancer recurrence and mortality may not be explained by differential declines in breast density due to ET.

Background and Aim: Reduction in breast density has been proposed as a biomarker of response to endocrine therapy (ET). The vast majority of current data are derived from white or Asian women. Because baseline breast density is associated with race, it is possible that changes in breast density with treatment may also be affected by race. Our objective was to assess the impact of ET on volumetric breast density (VBD) and fibroglandular volume (FGV) in African American (AA) women with invasive breast cancer. Methods: We conducted a retrospective study of AA women diagnosed with estrogen receptor positive invasive breast cancer at our institution from 2009-2013. Mammograms within two years prior to diagnosis and at least 6 months post-diagnosis were utilized for comparing density measurements. Using Volpara automated software, VBD and FGV were measured for the contralateral normal breast by averaging the respective values measured on the craniocaudal and mediolateral oblique views. Results: 51 women met the inclusion criteria and were confirmed to have received ET. Sixteen women received tamoxifen, 34 received an aromatase inhibitor, and medication data was unavailable in one case. The mean age at diagnosis was 56 years (range 29-72, median 55). 53% of women had stage I disease, 29% had stage II disease, and 18% had stage III disease. The majority of women had ER+ PR+ HER2 - disease (82.4%). 53.0% of women received systemic chemotherapy and all but one woman were treated surgically. Average body mass index (BMI) at diagnosis was 36.5, with data not available for 22 women. The mean time between diagnosis and baseline mammogram was 32 days, and the mean time between follow-up mammogram and baseline mammogram was 401 days. Average BMI at one year follow up was 33.7, with data not available for 19 women. The mean baseline VBD was 7.5% (range 1.9-21.5%, median 6.3%) and the mean follow-up VBD was 6.9% (range 2.0-23.6%, median 5.6%). Fifteen women had a longitudinal increase in VBD. The mean absolute change in VBD was -0.6% (range -3.4% to +9.8%, median 0.7%), with a mean 8.0 percent decrease from baseline to follow-up (range -0.7 to +0.5, median 0.1). The mean baseline FGV was 72.3 cm3 (range 18.5-208.4, median 65.3) and the mean follow-up FGV was 69.7 cm3 (range 22.7-197.5, median 60.5). Nineteen women had a longitudinal increase in FGV. The mean absolute reduction in FGV was 2.6 cm3 (range -53.3 to 49.3, median 4.8), with a mean 0.9 percent decrease from baseline to follow-up (range -111.6 to +53.0, median 5.2). Conclusions: We observed an overall decrease in Volpara-calculated VBD and FGV in our cohort of AA women treated with ET. It remains to be determined whether changes in VBD and FGV across serial mammograms may be a biomarker for response to ET in women of all races. Large prospective studies are needed to evaluate the effects of ET on longitudinal changes in VBD and FGV while controlling for confounders such as menopausal status, BMI, and chemotherapy. Citation Format: Johnson HM, Shivalingappa H, Wong JH, Muzaffar M, Verbanac K, Vohra NA. Longitudinal changes in volumetric breast density and fibroglandular volume with endocrine therapy in African American women with estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-11-12.