The relationship between mammographic density and duration of hormone therapy: effects of estrogen and estrogen–progestin

BACKGROUND: The purpose of this study was to examine the effects of duration of hormone therapy (HT) and treatment regimens on mammographic density. METHODS: A retrospective study was carried out of of 467 post-menopausal women who received estrogen or estrogen–progestin and had regular mammographic density determination by the Breast Imaging Reporting and Data System between 1994 and 2001. RESULTS: The fraction of women using HT who had an increase in mammographic density became more important over time. Further analysis of the effects of regimens after 4 years of HT shows that the increase in mean density was much greater in women receiving combined HT than in those receiving estrogen alone. The incidence of increased mammographic density showed significantly progressive increases over the duration of combined HT from 7.5 to 22.4%. CONCLUSIONS: Although most women using HT maintained breast density at pre-treatment levels, there is a note of caution for women using long-term HT, especially those using combined estrogen–progestin.