The effects of bazedoxifene on mammographic breast density in postmenopausal women with osteoporosis

Objective: This study aimed to assess quantitative changes in mammographic breast density after 24 months of therapy with bazedoxifene compared with raloxifene or placebo in postmenopausal women with osteoporosis. Methods: This was a retrospective, ancillary study of a subset of women enrolled in a multicenter, double-blind, randomized, placebo- and active-controlled phase 3 trial evaluating bazedoxifene for the treatment of postmenopausal osteoporosis. Participants were randomly assigned to receive bazedoxifene 20 or 40 mg, raloxifene 60 mg, or placebo once daily for 3 years. To be eligible for breast density evaluation, participants had to be 62 years or younger and completed 24 months of treatment, with mammograms at baseline and 24 months. Original mammogram pairs (left craniocaudal views) for each participant were digitized and analyzed by a radiologist. Breast density was measured using interactive thresholding to segment the mammogram, and percent density was determined using a validated software program. Results: Mammogram pairs were obtained from 444 participants. Baseline and demographic characteristics were similar among groups (mean age, 58.7 y). After 24 months, the mean percent changes in breast density from baseline were low (bazedoxifene 20 mg, -1.2%; bazedoxifene 40 mg, -0.4%; raloxifene 60 mg, -0.5%; placebo, -0.2%) and not significantly different among groups. Conclusions: Treatment with bazedoxifene for 2 years did not affect age-related changes in breast density in this population of postmenopausal women with osteoporosis. The changes in breast density with bazedoxifene 20 or 40 mg were similar to those with raloxifene 60 mg or placebo.