Effect of estrogen-progestin and estrogen on mammographic density.

OBJECTIVE: To assess the different effects between non-treatment, estrogen and estrogen-progestin regimens on changes in mammographic density in postmenopausal women.

STUDY DESIGN: A historical cohort of 105 postmenopausal women who attended the Menopause Clinic, Srinagarind Hospital, Khon Kaen, Thailand, and received 1 of 3 regimens: nontreatment, estrogen or estrogen-progestin (35 in each group). Mammographic examinations were done before and after a 12-24-month period of hormone therapy. Breast density (mammographic density, recorded in the medical records) between the 2 examinations in each group were compared.

RESULTS: An increase in mammographic density occurred among women receiving hormone therapy: 40% (14 of 35) in the estrogen-progestin group and 20% (7 of 35) in the estrogen-only group, but no variation in density was observed in the nontreatment group. The increase in mammographic density occurring in women on hormone therapy, as compared to the nontreatment group, was statistically significant (estrogen-progestin, 95% CI 20.91-59.09; estrogen, 95% CI 3.89-36.11). When the different treatment types were compared, the estrogen-progestin group tended to have a higher prevalence of mammographic density change than the estrogen-only group, but the difference was not statistically significant (95% CI -3.81-43.81).

CONCLUSION: Hormone therapy was associated with increased mammographic density. Apparently the estrogen-progestin regimen affects breast density more than estrogen-only does.