The largest North American breast cancer prevention trial, the Study of Tamoxifen and Raloxifene, or STAR trial, has compiled an initial analysis of study data and found the osteoporosis drug raloxifene works as well as tamoxifen in reducing breast cancer risk for postmenopausal women at increased risk of the disease. Both drugs reduced the risk of developing invasive breast cancer by about 50 percent.

Tamoxifen (trade name Nolvadex®) ushered in the field of breast cancer chemoprevention. It has been used to treat women with breast cancer for more than 20 years, and based on findings from the landmark Breast Cancer Prevention Trial (BCPT), the drug was approved for use in 1998 to also help prevent breast cancer in women at high risk of developing the disease. But at about the same time, raloxifene (trade name Evista®), a drug approved to treat and prevent osteoporosis, also was found to reduce breast cancer incidence.

Both drugs - taken in pill form - manipulate a cell's use of the estrogen hormone, which can fuel the growth of tumors in breast tissue.

To test whether either of the drugs can offer superior protection against breast cancer, STAR was launched in 1999 by the non-profit research group, the National Surgical Breast and Bowel Project (NSABP), and was funded by the National Cancer Institute. In all, 19,747 women participated in the STAR clinical trial.