Race May Not Impact Endocrine Therapy–Related Changes in Breast Density

Abstract

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.