Mammographic breast density during hormone replacement therapy: effects of continuous combination, unopposed transdermal and low-potency estrogen regimens

Abstract

Objective: The aim of this study was to evaluate the impact of different hormone replacement therapy (HRT) regimens on mammographic breast density.Study design: Mammographic density wasrecorded in women participating in a population-based screening program. At first mammogram, all women were non-users of HRT, and thereafter reported continuous use of the same HRT regimen. The study populationcomprised 158 women: a total of 52 women were using continuous combined HRT (conjugated equine estrogen 0.625 mg plus medroxyprogesterone acetate 5 mg); 51 women were using low-dose oral estrogen alone(estriol 2 mg daily); and 55 women were using unopposed transdermal estrogen given as a patch (estradiol 50 μg/24 h). Films were coded and analyzed for mammographic density by an independent radiologistblinded to treatments. Mammographic density was classified according to Wolfe.Results: An increase in mammographic density was much more common among women taking continuous combined HRT (40%)than for those using oral low-dose estrogen (6%) and transdermal (2%) treatment. The increase in density was already apparent at the first visit after starting HRT. During long-term follow-up, there wasvery little change in mammographic status.Conclusion: HRT regimens were shown to have different effects on the normal breast. There is an urgent need to clarify the biological nature and significanceof a change in mammographic density during treatment and, in particular, its relation to symptoms and breast cancer risk.