[Antiestrogens and normal human breast cell proliferation]

Steroidal (progestins) and non steroidal antiestrogens (tamoxifen and derivatives) are strong antiproliferative molecules when added to normal human breast cells in culture. The antiproliferative action of tamoxifen and 4-hydroxytamoxifen isomers is comparable to that observed in cultured breast cell lines. The progestin promegestone (R 5020) is a strong antiproliferative agent in the presence as well as in the absence of estradiol. Identically, at higher concentration the antiprogestin RU 486 slows down cell proliferation probably due to its progesterone agonist activity. Both progestins and antiprogestins stimulate 17 beta-hydroxysteroid dehydrogenase activity, a marker of progesterone receptor but only in estradiol primed cells.