Predictors of breast density change after hormone therapy cessation: results from a randomized trial.

BACKGROUND Postmenopausal hormone therapy 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 hormone therapy cessation. METHODS Postmenopausal hormone therapy users with a prior screening mammogram (n = 1,168) were randomized to continue hormone therapy or to suspend hormone therapy for 1 month or 2 months before their next screening mammogram. We estimated relative risks (RR) and attributable risks with 95% CIs of a ≥7.5% decrease in percentage MD (%MD) versus no change associated with hormone therapy cessation, stratified by age, body mass index (BMI), parity, and other factors. RESULTS Hormone therapy 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, hormone therapy type, or duration of hormone therapy use. CONCLUSIONS Woman-level factors do not appear to explain why some women experience a decrease in %MD following hormone therapy cessation and others do not. IMPACT We were unable to identify subgroups of women who are more likely to experience a decrease in MD due to hormone therapy cessation; other factors, such as genetic factors, may be important determinants of hormone therapy-related changes in MD.