Objectives: to evaluate the effects of different types of hormone replacement therapy (HRT) on mammographic density in postmenopausal women.
Methods: In a prospective 1-year study, 121 healthy postmenopausal women were allocated to one of the following five study groups: twenty-six women were treated with continuous transdermal 17beta-estradiol 50 mcg/die plus acetate nomegestrolo 5 mg/die sequentially added for 12 days per month (Group A); 25 women were treated with continuous transdermal 17beta-estradiol 50 mcg/die plus acetate nomegestrolo 2.5 mg/die added every day (Group B); 23 women were treated with continuous transdermal 17beta-estradiol 50 mcg/die (Group C); 24 women were treated with tibolone 2.5 mg/die (Group D); and 23 women not receiving any medication represented the control group (Group E). At the time of recruitment and after 12 months a two-view mammography was performed to evaluate mammographic density according to a quantitative method: type 1 (less than 25% of mammary gland covered by dense tissue), type 2 (from 25 to 75% of total glandular area covered by dense tissue), type 3 (more than 75% of mammary parenchyma covered by dense tissue).
Results: After 12 months of HRT, seven out of 20 patients (35%) in group A, nine of 21 patients (42.85%) in group B, four out of 19 patients (21%) in group C and two of 20 patients (10%) in group D, showed an increase in mammographic density. No variation of density was observed at the second mammographic test in the control group. The mammographic density increase which occurred in groups A, B and C was statistically significant (P<0.05) when compared with group E; no statistically significant difference (P=0.49) was found in mammographic density increase between group D and group E. When the different treatment types were compared each other, a statistically significant difference (P=0.04) was found only between the mammographic density increase occurring in groups B and D.
Conclusions: HRT may cause an increase of mammographic density. The frequency of the density increase is related to the type of HRT and a replacement therapy including a progestin, especially in continuous combination with estrogen, leads to more evident mammographic changes. Tibolone does not significantly affect mammographic density.