Initial results of the Study of Tamoxifen and Raloxifene, or STAR, show that the drug raloxifene (Evista), currently used to prevent and treat osteoporosis in postmenopausal women, works 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%. In addition, women who were prospectively and randomly assigned to take raloxifene daily, and who were followed for an average of 4 years, had 36% fewer uterine cancers and 29% 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.
One of the largest breast cancer prevention clinical trials ever conducted, STAR enrolled 19,747 postmenopausal women who were at increased risk of the disease. Participants were randomly assigned to receive either
60 mg of raloxifene or 20 mg of tamoxifen daily for 5 years. The trial is coordinated by the National Surgical Adjuvant Breast and Bowel Project (NSABP) and sponsored by the National Cancer Institute (NCI).
"This optimistic news from STAR is a significant step in breast cancer prevention," said John E. Niederhuber, MD, currently providing leadership at NCI. "These results, once again, demonstrate the critical importance of clinical trials in our efforts to establish evidence-based practices."
"In 1998, the landmark Breast Cancer Prevention Trial showed that tamoxifen could reduce the risk of invasive breast cancer in premenopausal and postmenopausal women by nearly 50%," said Norman Wolmark, MD, NSABP chairman. "Today, we can tell you that for postmenopausal women at increased risk of breast cancer, raloxifene is just as effective, without some of the serious side effects known to occur with tamoxifen."
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, MD, 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.