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.

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.

Participants in STAR are now receiving information about which drug they were taking.  Women assigned to raloxifene will continue to be provided with the drug until they have completed five years of treatment. Those women assigned to tamoxifen can choose to continue taking tamoxifen or to receive raloxifene to complete their five years of treatment.

Women taking either drug had equivalent numbers of strokes, heart attacks, and bone fractures. Both raloxifene and tamoxifen are known to protect bone health; it is estimated that half a million postmenopausal women are currently taking raloxifene by prescription to prevent or treat osteoporosis. Additionally, the initial results from STAR suggest that raloxifene does not increase the risk of developing a cataract, as tamoxifen does.

"Although no drugs are without side effects, tamoxifen and raloxifene are vital options for women who are at increased risk of breast cancer and want to take action," said Leslie Ford, M.D., associate director for clinical research in NCI's Division of Cancer Prevention. "For many women, raloxifene's benefits will outweigh its risks in a way that tamoxifen's benefits do not."

The STAR researchers also tracked known menopausal side effects that occur with both drugs and monitored the participants' quality of life. The data show that side effects of both drugs were mild to moderate in severity, and quality of life was the same for both drugs.

SOURCE:
University of Texas M.D. Anderson Cancer Research Center (http://www.mdanderson.org)