The fact that tamoxifen (Nolvadex®) blocks the action of estrogen in breast tissue while mimicking the action of estrogen in the uterus means that it functions as a SERM, selectively blocking or stimulating the estrogen receptors of different target tissues.
In addition to acting like estrogen in the uterus, tamoxifen resembles estrogen in its ability to lower LDL cholesterol levels. And in postmenopausal women, tamoxifen also resembles estrogen in its ability to preserve or increase bone density. Thus, aside from its tendency to increase the risk of uterine cancer, tamoxifen has a number of potentially beneficial properties.
As a result, scientists have been actively working on the development of other SERMs that might exhibit some of the beneficial properties of tamoxifen without sharing its potentially harmful effects.
Because of the potential cancer and cardiovascular risks inherent in hormone pills containing estrogen and progestin, scientists are working on the development of SERMs for postmenopausal women that can mimic the beneficial effects of estrogen without exerting any of its harmful effects.
The ideal drug, of course, would be a SERM exhibiting the positive effects of estrogen on bones, heart, and blood vessels without exhibiting the potentially harmful effects of estrogen on the breast and uterus.