RESUMEN
OBJECTIVE: To assess long-term effects of different hormone replacement therapy (HRT) regimens on mammographic density. METHODS: One hundred sixty-five postmenopausal women were treated with the same HRT during 5 years: 38 received transdermal estradiol, 78 cyclic combined therapy and 49 continuous combined therapy. Mammograms were obtained at baseline, at 1-year and 5-year treatment. Breast density changes were categorized as slight focal increased density, considerable focal increased density, slight diffuse increased density and considerable diffuse increased density. RESULTS: Mammographic density increased in 7.9% of women receiving estrogen alone versus 25.2% of women receiving combined therapy (p < 0.022) during 1 year, and in 7.9% of women versus 28.3% of women (p < 0.009) after 5 years of therapy, respectively. There were significant statistical differences in women treated with estrogen alone versus those treated with combined HRT after 1 and 5 years. After 5 years of HRT, breast density increased 21.8% in women receiving cyclic combined therapy versus 38.8% in those under continuous combined therapy (p < 0.039). CONCLUSION: An increase in breast density is significantly more frequent in women receiving combined estrogen-progestin therapy than in women receiving estrogen alone. There are differences between cyclic and continuous combined therapy at 5 years of treatment.