[Antiestrogen action of progesterone in the breast]

This review analyzes recent data from international literature concerning the antiestrogen action of progesterone, progestins and the antiprogesterone RU 486 at the level of mammary cells in culture from either breast cancer lines or normal breast obtained from reduction mammoplasties. Most data indicate that progesterone, progestins and even RU 486 have a strong antiestrogen effect on breast cell appreciated by the decrease of estradiol receptor content, the decrease of cell multiplication and the stimulation of 17 beta-hydroxysteroid activity which may be considered as a marker of breast cell differentiation dependent of progesterone receptor.