Estradiol and progesterone regulate the proliferation of human breast epithelial cells

Objective: To study the effects of estradiol and progesterone on the proliferation of normal human breast epithelial cells in vivo. Design: Double-blind randomized study. Setting: Department of gynaecology and of cell biology at a university hospital. Patient(s): Forty postmenopausal women with untreated menopause and documented plasma FSH levels of > 30 mlU/mL and estradiol levels of < 20 pg/mL. Intervention(s): Daily topical application to both breasts or a gel containing a placebo, estradiol, progesterone, or a combination of estradiol and progesterone during the 14 days preceding esthetic boast surgery or excision of a benign lesion. Main Outcome Measure(s): Plasma and breast tissue concentrations of estradiol and progesterone. Epithelial cell cycles were evaluated in normal breast tissue by counting mitoses and performing quantitative proliferating cell nuclear antigen immunolabeling analyses. Result(s): Increasing the estradiol concentration enhanced the number of cycling epithelial cells, whereas increasing the progesterone concentration significantly limited the number of cycling epithelial cells. Conclusion(s): Exposure to progesterone for 14 days reduced the estradiol-induced proliferation of normal breast epithelial cells in vivo. (C) 1998 by American Society for Reproductive Medicine.