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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:
- Women at high risk of breast cancer (as determined by family history, age, etc.) should
discuss the use of tamoxifen with their physicians and be informed about the benefits and
risks of using drugs to help prevent breast cancer.
- Women at low or average risk of developing breast cancer should not be offered tamoxifen
or raloxifene because the potential risks of these drugs may be greater than their
benefits
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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