Aim: To evaluate the effects of different regimens of hormone replacement therapy (HRT) on mammographic breast density.
Methods: Mammograms of 113 healthy postmenopausal women who were on different HRT regimens were evaluated retrospectively. All women had a baseline mammography and at least one mammogram after at least 12 months of HRT. Four parenchymal patterns were considered mammographically. Quantification of density changes that occurred on follow-up mammograms was done qualitatively and with reference to densities on baseline mammograms.
Results: Sixty women were treated with a continuous estrogen-progestin combination; 16 with a cyclic estrogen-progestin combination and 37 were with estrogen only. Twenty-six women had increased mammographic density after HRT. Mammographic density increase was detected in 23 women (38.3%) of the continuous estrogen-progestin combination group, two women (12.5%) of the cyclic estrogen-progestin combination group and one woman (2.7%) of the estrogen-only group. Mammographic density increase was more common among women in the continuous estrogen-progestin combination group than the other groups and this difference was found to be statistically significant (P < 0.001). Breast density increase was observed in 18 of 30 women (60%) with higher doses of progestin compared to 5 of 30 women (16.7%) with lower dose (P < 0.05).
Conclusions: Postmenopausal HRT may increase mammographic breast density. Breast density appears to be mostly affected by higher doses and continuous administration of progestin.