Progestin may modify the effect of low-dose hormone therapy on mammographic breast density.

OBJECTIVES

To evaluate the effect on breast density of two low-dose hormone therapy regimens identical in their estrogen component but different in the progestin.

METHODS

A total of 81 non-hysterectomized postmenopausal women were allocated either to 17beta-estradiol 1 mg and norethisterone acetate 0.5 mg (E2/NETA, n = 43) or to 17beta-estradiol 1 mg and drospirenone 2 mg (E2/DRSP, n = 38). Treatment was continuous and lasted 12 months. The main outcomes were the changes in breast density according to the Wolfe classification between baseline and 12-month mammograms.

RESULTS

Involution of the fibroglandular tissue was not seen in either of the treatment groups. Under E2/NETA, breast density increased in seven women (16.3%). In contrast, only three women (7.9%) exhibited a density increase under E2/DRSP.

CONCLUSIONS

Although hormone therapy appears to suspend breast involution, it does not increase breast density in the majority of treated women. Progestins differing in pharmacological properties may have a variable impact on breast density.