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Cancer Causes Control. 2006 Dec;17(10):1227-35.

Do breast cancer risk factors modify the association between hormone therapy and mammographic breast density? (United States).

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Group Health Center for Health Studies, Suite 1600, Seattle, WA 98101, USA.



To evaluate whether the association between hormone therapy (HT) and breast density differs by levels of breast cancer risk factors.


We evaluated 80,867 screening mammograms from 39,296 postmenopausal women from Washington State. We estimated odds ratios and 95% confidence intervals for dense breasts (Breast Imaging Reporting and Data System categories 3 "heterogeneously dense" and 4 "extremely dense") compared to fatty breasts (categories 1 "almost entirely fat" and 2 "scattered fibroglandular") among HT users compared to never users. We separately examined former HT use and current HT use by type (estrogen plus progestin therapy (EPT) and estrogen-only therapy (ET)). We stratified the associations by age, BMI, race, family history, and reproductive and menopausal factors.


Current EPT users had a 98% (1.87-2.09) greater odds of having dense breasts and current ET users had a 71% (1.56-1.87) greater odds compared to never users. Current HT users were more likely to have dense breasts if they were older, had more children, or younger at first birth compared to never users; these associations were stronger among EPT users than ET users.


HT, particularly EPT, may reduce protective effects of older age, parity, and younger age at first birth on mammographic density.

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