[The in vivo effect of the local administration of progesterone on the mitotic activity of human ductal breast tissue. Results of a pilot study].

Breast tissue samples were taken during surgery in premenopausal women with various benign breast diseases. Surgery was scheduled between day 11 to 13 of their menstrual cycle, before presumed ovulation and endogenous production of progesterone. Each patient was treated 11 to 13 days before surgery by daily percutaneous topical application on breast of either a placebo gel, a gel containing progesterone or a gel containing estradiol. Treatments were assigned at random and the study conducted double-blind. The mean estradiol concentration in breast tissue was significantly higher (3,409 pg/g) in the estrogen-treated group than in the placebo (365 pg/g) and the progesterone (523 pg/g) treated groups. The mean progesterone concentration in breast tissue was significantly higher (69.1 ng/g) in the progesterone treated group than in the placebo (1.95 ng/g) and the estradiol (3 ng/g) treated groups. Mitotic activity was calculated by counting with light microscopy mitoses in epithelial cells of normal lobular area. Mean mitotic activity was significantly lower in progesterone treated group (0.04/1,000 cells) than in placebo (0.10/1,000 cells) or in estradiol (0.22/1,000 cells) treated groups. High concentration of progesterone sustained in human breast tissue in vivo during 11 to 13 days does not increase, but actually decreases mitotic activity in normal lobular epithelial cells.