Abstract P2-08-10: Mammographic breast density changes with endocrine therapy (ET) in women with hormone receptor positive (HR+) breast cancer in a Utah population
Authors: Wei Mei , Pappas Lisa , Guinto Emily , Sweeney Carol , Camp Nicola , Freer Phoebe , Buys Saundra , Henry N. Lynn , Curtin Karen 
Published: March 2020

Abstract
Introduction: Women with extremely dense breast tissue on mammography have a higher risk of breast cancer compared to similarly-aged women with less dense breast tissue. Tamoxifen therapy has been observed to reduce breast density among both pre- and postmenopausal women with HR+ breast cancer and may predict benefit of therapy. Studies of aromatase inhibitor (AI) therapy and breast density change, however, are limited and results inconclusive. Factors associated with breast density change with ET, and effect of duration of ET on breast density change, have not been well studied.
Methods: Using the Utah Population Database, women were identified who underwent screening mammography in 2005-2016 and who had no personal history of breast cancer. Those who were subsequently diagnosed with HR+ breast cancer and treated in one of the major health care systems in Utah (Intermountain Healthcare or University of Utah Health) were included in the analysis. ET prescription information and duration of ET were obtained from provider records and the Utah All-Payer Claims Database. Women with mammography results in the electronic medical record both before and within 3 years after the breast cancer diagnosis were included. BI-RADS density classification from mammogram reports 6-12 months, 13-24 months, and 25-36 months after ET initiation were compared to pre-diagnosis BI-RADS density classification. Breast density reduction was defined as a decrease of ≥1 BI-RADS category compared to baseline. Fisher’s exact test was used to examine ET and breast density reduction among women ≥55y and &lt;55y.
Results: In total, 1328 women with HR+ breast cancer and baseline BI-RADS breast density categories B-D were included. Women with BI-RADS density category A(almost entirely fatty) were excluded. A majority (61%) were age ≥55y at diagnosis, were non-Hispanic white (90%), and had BMI ≥25 kg/m2 (56%); 15% had a first-degree family history of breast cancer. At baseline, 602 (44%) women had scattered fibroglandular densities (BI-RADS category B), 697 (50%) had heterogeneously dense breasts (BI-RADS category C), and 83 (6%) had extremely dense breasts (BI-RADS category D). Half were treated with AI only (49%), 21% with tamoxifen only, and 29% with both during follow-up. In both the age ≥55y and &lt;55y groups, women with BI-RADS category D at baseline were more likely to experience a reduction in breast density with ET compared to women with either BI-RADS categories B or C (Table 1). There were no significant differences in breast density reduction observed between women treated with AI only compared to those treated with tamoxifen only, irrespective of age and baseline density. Breast cancer family history also had no effect on breast density reduction with ET.
Conclusion: Baseline breast density is associated with a demonstrable reduction in breast density during ET. Our findings suggest that AI therapy can reduce breast density similar to that seen with tamoxifen therapy.
Table 1 Breast Density (BD) changes among women who underwent mammography 6-12 months, 13-24 months, and 25-36 months after ET initiationBaseline BDN≥55 years oldPTotal&lt;55 years oldPNo BD reduction N(%)BD reduction N(%)No BD reduction N(%)BD reduction N(%)6-12 months after ET initiationScattered157152(97)5(3)5452(96)2(3)Heterogeneous148115(78)33(22)10477(74)27(26)Dense144(29)10(71)&lt;0.0001248(33)16(67)&lt;0.0001Total319271(85)48(15)182137 (75)45(25)13-24 months after ET initiationScattered232214(92)18(8)8473(87)11(13)Heterogeneous211144(68)67(32)155107(69)48(31)Dense172(12)15(88)&lt;0.0001287(25)21(75)&lt;0.0001Total460360(78)100(22)267187(70)80(30)25-36 months after ET initiationScattered248220(89)28(11)8374(89)9 (11)Heterogeneous203133(66)70(35)16097(61)63(39)Dense162(13)14(88)&lt;0.00013213(41)19 (59)&lt;0.0001Total467355(76)112(24)275184(67)91(33)
Citation Format: Mei Wei, Lisa Pappas, Emily Guinto, Carol Sweeney, Nicola Camp, Phoebe Freer, Saundra Buys, N. Lynn Henry, Karen Curtin. Mammographic breast density changes with endocrine therapy (ET) in women with hormone receptor positive (HR+) breast cancer in a Utah population [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-08-10.