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Upon analyzing new data on breast cancer prevention strategies, a panel of cancer experts recommended that physicians discuss the benefits of the drug tamoxifen with patients at high-risk for breast cancer. However, the panel concluded that women at average or low risk for breast cancer should not take tamoxifen because, in many cases, the benefits of the drug do not outweigh the potential risks. The panel also found that the osteoporosis drug raloxifene (brand name, Evista) shows benefit in preventing breast cancer in high-risk women. However, the panel said that further data are needed before raloxifene can be recommended for breast cancer prevention. The U.S. Preventive Services Task Force is an independent panel of experts sponsored by the Agency for Healthcare Research and Quality (AHRQ). The panel based its recommendations on a report published by a research team led by Linda Kinsinger, MD, MPH and Russell Harris, MD., MPH of AHRQ's Evidence-based Practice Center at the RTI International and the University of North Carolina. The report dealt with chemoprevention—drugs used to help lower the risk of developing breast cancer. "Researchers have long known that tamoxifen can reduce the chances for a second episode of breast cancer in women who have already had breast cancer. But only recently have studies been done to see whether medications can reduce breast cancer risk in healthy women who are at high risk for the disease," said Janet Allan, PhD, RN, vice chair of the Task Force, in an AHRQ press statement. "The Task Force found fair evidence that tamoxifen can significantly reduce the risk for invasive estrogen-receptor-positive breast cancer by approximately 50 percent in women at high risk for the disease. We found consistent evidence for raloxifene, but it was limited to one study that focused on use of the drug to prevent fractures." Four chemoprevention clinical trials were analyzed by the panel. Three of the trials involved the use of tamoxifen in women who did not have breast cancer, and the other trial involved the drug raloxifene. Both tamoxifen and raloxifene belong to the same class of drugs, called SERMS (selective estrogen receptor modulators), which are thought to prevent breast cancer by blocking the hormone estrogen from estrogen receptors in breast cancer cells. The largest trial analyzed by the panel, the Breast Cancer Prevention Trial (BCPT), involved 13,388 women. As Dr. Allan said, the study found a 49% reduction in breast cancer risk among women at high risk of breast cancer who used tamoxifen. The two other tamoxifen trials did not show that the drug decreased breast cancer risk; however, the panel said that the BCPT trial was by far the largest and most accurate of the studies. The study of raloxifene did not involve women at high risk of breast cancer. Instead, it evaluated the use of raloxifene in post-menopausal women with osteoporosis, a bone-thinning disease that increases the risk of fractures. However, the study found that raloxifene reduced the risk of breast cancer by 76% in addition to treating osteoporosis. Nevertheless, the panel said that results of a trial that specifically studied breast cancer risk reduction with raloxifene was needed before the drug could be recommended to help prevent breast cancer. The STAR trial (Study of Tamoxifen and Raloxifene) is currently underway and analyzing both drugs in 22,000 post-menopausal women at high risk for breast cancer. Summary of the panel’s findings:
The potential risks of tamoxifen include endometrial cancer (cancer of the lining of the uterus), deep vein thrombosis (blood clots in large veins, particularly in the legs), pulmonary embolism (blood clot in the lung), and possibly stroke. The current STAR trial is evaluating the potential risks of raloxifene.
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