Isomers of broparoestrol and antiestrogen action: comparison with tamoxifen.

This study compares the relative biological potencies of a known antiestrogen tamoxifen to two triarylethylene compounds which have been shown previously to be potent inhibitors of rodent mammary tumorigenesis. Based on a) uterotrophic and anti-uterotrophic tests, b) indexes of cellularity, and c) protein content, these studies indicate that the trans, as well as the cis, isomers of bromotriphenylethylene are partial estrogen antagonists with no estrogenic effects in rat uteri and partial agonists in mouse uteri, whereas tamoxifen shows partial antiestrogenic/estrogenic effects in rats and is fully estrogenic in mice.