Background: Mammographic density adversely affects diagnostic accuracy and may be a risk factor for breast cancer. Mammographic density is affected by hormone replacement therapy (HRT).
Objective: To assess mammographic density in postmenopausal women with and without HRT.
Method: Part I. Mammographic density was determined in 1232 postmenopausal women attending a breast screening clinic. Density was compared between HRT users and nonusers in three age groups. When available, previous mammograms were assessed for interval density change. Part II. Density change in 162 women during transition from premenopause to postmenopause was recorded. HRT effect was assessed.
Results: Part I. There was no density difference between postmenopausal HRT-users and nonusers younger than age 55. Thereafter, the density was significantly less in nonusers. In the majority of HRT-users the density remained at pretreatment levels but density increased in 8% of women after HRT was started. Part II. Of 117 HRT nonusers followed over menopause 38% had a density decrease before age 55. Of those started on HRT, 80% had no density change, 18% decreased density and 2% increased density.
Conclusions: The density decreases significantly after age 55 with the greatest change occurring between age 55 and 64. This decrease does not occur in the majority of HRT-users. Usually HRT maintains the density present at the time HRT is started. Density decreases after HRT is started in some women suggesting refractoriness to hormones. In fewer than 8% of women density increases commensurate with HRT. Any adverse effect of HRT may depend on the receptivity of the epithelial elements which, in turn, may be reflected by the mammographic density at the time HRT is started.