Mammographic breast density during hormone replacement therapy: Differences according to treatment

OBJECTIVE: Our purpose was to investigate the effects of various hormone re placement regimens on mammographic breast density. STUDY DESIGN: Mammographic density was recorded in women participating in a population-based screening program. AII women were nonusers of hormone rep lacement therapy at first mammogram and thereafter reported continuous use of the same treatment: estrogen alone (n = 50) or estrogen in cyclic (n = 7 5) or continuous (n = 50) combination with progestogen. Mammographic densit y was quantified according to the Wolfe classification. RESULTS: An increase in mammographic density was much more common among wom en receiving continuous combination hormone replacement therapy (52%) than among those receiving cyclic (13%) and estrogen-only (18%) treatment. The i ncrease in density was apparent already at first visit after the start of h ormone replacement therapy. There was little change in mammographic status during long-term follow-up. CONCLUSION: Regimens of hormone replacement therapy were shown to have diff erent effects on the normal breast. There is an urgent need to clarify the biologic nature and significance of a change in mammographic density during treatment and, in particular, its relation to symptoms and breast cancer r isk.