Postmenopausal hormone therapy (HT) cessation is associated with a decrease in mammographic density (MD), but it is unknown whether this effect is modified by woman-level characteristics. We investigated whether we could identify characteristics of women who were most likely to experience a decrease in MD due to HT cessation.
Postmenopausal HT users with a prior screening mammogram (n=1,168) were randomized to continue HT, or to suspend HT for 1 month or 2 months before their next screening mammogram. We estimated relative risks (RR) and attributable risks with 95% confidence intervals (CI) of a ≥7.5% decrease in percentage MD (%MD) versus no change associated with HT cessation, stratified by age, BMI, parity, and other factors.
HT cessation increased a woman’s likelihood of experiencing a ≥7.5% decrease in %MD by 30% (95% CI=1.03–1.7), but we found little evidence of effect modification by age, race, BMI, change in BMI, baseline %MD, parity, family history of breast cancer, HT type, or duration of HT use.
Woman-level factors do not appear to explain why some women experience a decrease in %MD following HT cessation and others do not.
We were unable to identify subgroups of women who are more likely to experience a decrease in MD due to HT cessation; other factors, such as genetic factors, may be important determinants of HT-related changes in MD.
Keywords: breast density, mammographic density, hormone therapy, cessation, breast cancer