Prolonged oestrogenic and mitogenic activity of tamoxifen in the ovariectomized mouse.

A dose of tamoxifen (ICI 46,474), which has been found to inhibit the vaginal smear response to oestrogens, exerted prolonged oestrogenic effects in mice and increased the rate of cell proliferation in both the vagina and uterus. The vaginal epithelium became multilayered with stratified or cornified surface layers and the uterus developed gross cystic glandular hyperplasia. This demonstrates that ICI 46,474 is simply a weak oestrogen in the mouse.