Neutral effect of ultra-low-dose continuous combined estradiol and norethisterone acetate on mammographic breast density

Objective To compare the effects of two different ultra-low doses of continuous combined hormone therapy and placebo on mammographic breast density in postmenopausal women. Methods A subpopulation of 255 postmenopausal women from the CHOICE trial were randomly assigned to 0.5 mg 17 beta-estradiol (E2) + 0.25 mg norethisterone acetate (NETA), 0.5 mg E2 + 0.1 mg NETA, or placebo. Women using hormone replacement therapy (HRT) up to 2 months prior to the study were excluded; 154 women fulfilled the inclusion criteria. Mammograms were performed at baseline and after 6 months. Breast density was evaluated by visual classification scales and a computer-assisted digitized technique. Results No significant differences were detected between the active treatment groups and the placebo group in the digitized quantification. The mean baseline values for density around 20% were unchanged after 6 months. Also, visual classifications showed no increase in breast density in any study group. Conclusion In contrast to currently available bleed-free regimens, the new ultra-low-dose combination of 0.5 mg E2 and 0.1 mg NETA seems to have very little or even a neutral effect on the breast. Both digitized quantification and visual assessment of breast density were unchanged after 6 months. Larger prospective studies should be performed to confirm this new finding.