The U.S. Preventive Services Task Force has recommended that clinicians discuss the potential benefits and risks of taking prescription medicines such as tamoxifen to reduce the risk of breast cancer with their female patients who are at high risk for the disease. The Task Force also recommended against the use of these drugs by women at low or average risk for breast cancer.

The Task Force, an independent panel of experts that is sponsored by the Agency for Healthcare Research and Quality (AHRQ), reviewed three randomized controlled trials that studied the use of the drug tamoxifen and one study on the off-label use of the drug raloxifene to reduce the risk of breast cancer (known as "chemoprevention"). The Task Force's two recommendations were published in the journal Annals of Internal Medicine.

"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, Ph.D., R.N., vice chair of the Task Force. "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."

Tamoxifen is the only medication currently approved by the U.S. Food and Drug Administration (FDA) to reduce the incidence of breast cancer in women at high risk for breast cancer. Raloxifene currently is approved by the FDA for the prevention and treatment of osteoporosis, but some clinicians prescribe it off-label to reduce the risk of breast cancer. The Study of Tamoxifen and Raloxifene (STAR), an ongoing trial by the National Cancer Institute (NCI), is recruiting post-menopausal women at increased risk for breast cancer to compare the safety and efficacy of the two drugs in reducing the risk of the disease. Information about the trial can be found at http://www.cancer.gov/star.

Women are considered at high risk for breast cancer if they are over 40 and have a family history of breast cancer in a mother, sister, or daughter or have a history of atypical cells on a breast biopsy. A risk assessment instrument developed by NCI (http://www.cancer.gov/bcrisktool) can help estimate cancer risk based on age, family history, and other risk factors.

For women who are not at high risk for developing breast cancer, the Task Force recommended against the routine use of tamoxifen or raloxifene to reduce the risk of breast cancer because the potential harmful side effects may outweigh the potential benefits. Those side effects can include hot flashes and increased risk for blood clots in the legs or lungs. Tamoxifen also has been found to increase the risk for endometrial cancer.

In general, the Task Force found that the balance of benefits and harms of chemoprevention is more favorable for women in their 40s who are at high risk for breast cancer and have no predisposition toward blood clots, and for women in their 50s who are at high risk for breast cancer, who have no predisposition to blood clots, and who do not have a uterus. However, each woman needs to talk with her clinician about whether the potential benefits of reducing her risk for breast cancer are worth the potential risks of the medications.

SOURCES:
Agency for Healthcare Research and Quality (http://www.ahrq.gov)
Annals of Internal Medicine, July 2, 2002