On Apr. 17, 2006, the National Cancer Institute (NCI) announced initial results of the Study of Tamoxifen and Raloxifene, or STAR, showed that the drug raloxifene, used to prevent and treat osteoporosis in postmenopausal women, worked as well as tamoxifen in reducing breast cancer risk for postmenopausal women at increased risk of the disease.

In STAR, both drugs reduced the risk of developing invasive breast cancer by about 50 percent. In addition, within the study, women who were prospectively and randomly assigned to take raloxifene daily, and who were followed for an average of about four years, had 36 percent fewer uterine cancers and 29 percent fewer blood clots than the women who were assigned to take tamoxifen. Uterine cancers, especially endometrial cancers, are a rare but serious side effect of tamoxifen. Both tamoxifen and raloxifene are known to increase a woman’s risk of blood clots.