The report details findings on bone function, blood cholesterol and uterine tissues in rats. Further research on animals and in the lab indicates that GW5638 works as an anti-estrogen in breast cells, the researchers said. Now we find the action of estrogen in bones and the cardiovascular system is very different than in the breast and uterus, and this compound appears to offer us estrogen's benefits. As an expert on the estrogen hormone, McDonnell's goal was to find a new compound that functions as an anti-estrogen in the breast and uterus. Although the process is not well understood, estrogen apparently targets a cellular gene in breast tissue that causes proliferative growth.
Tamoxifen works by blocking the action of estrogen, and so the growth of cancer.
It is called a chemotherapy because it helps halt the spread of cancer, but it differs from other chemotherapy that kills tumors through toxic chemicals. Other women never respond to tamoxifen at all. McDonnell wanted to find a substitute for estrogen that would halt cancer growth in breast tissue but not pose a threat of uterine cancer. He said he also hoped the compound would offer the benefits of natural estrogen to organs and tissues that need it, such as bone cells and the cardiovascular system, without the risks of estrogen. Natural estrogen also poses an increased risk of uterine cancer, and possibly of breast cancer, in post-menopausal women who want to use hormone supplements to protect bone strength.