Women at high risk of breast cancer can often lower that risk by taking medication, including drugs like tamoxifen or the osteoporosis drug raloxifene (Evista).
About 2 percent of U.S. women are at high risk for breast cancer, but few take risk-lowering drugs.
Now, a new analysis suggests that women and their doctors need to weigh the dangers of the drugs' side effects -- which can include blood clots, cataracts, and cancer of the uterine lining -- against the benefits of breast cancer prevention.
The analysis, funded by the U.S. Department of Health and Human Service's Agency for Healthcare Research and Quality, was published in the September 15 issue of Annals of Internal Medicine.
However, the bigger problem may be that not enough women who are candidates for the drugs are actually taking them. About 2 percent of U.S. women are at high risk for breast cancer, but many don't take tamoxifen or raloxifene, according to Dr. Christy Russell, an American Cancer Society spokesperson who chairs the organization's breast cancer advisory committee. Health.com: What keeps your breasts healthy
"That's extremely unfortunate, because we have 200,000 new cases of invasive breast cancer every year and we could potentially reduce that number by half using drugs that are already approved by the [Food and Drug Administration] for this specific purpose," she says. Russell says the drugs are underused due to a lack of education among both patients and physicians as to their safety and effectiveness.
"As a culture, it's a very hard sell to convince us to take drugs for a disease we don't already have," she adds. Health.com: Dogs sniff out clues in the fight against cancer
In the new review, Dr. Heidi Nelson, of the Oregon Health & Science University, and her colleagues looked at eight clinical trials of three drugs -- tamoxifen, raloxifene, and tibolone. The trials were all conducted in women at high risk of breast cancer who had not been diagnosed with the disease.
Tamoxifen and raloxifene are both selective estrogen-receptor modulators (SERMs), a class of drug that cuts the risk of invasive breast cancer in at-risk women. Both drugs are FDA-approved for that purpose. Tibolone works in a different way and is not approved for use in the United States. (It is approved for menopausal symptoms in 90 countries, and for osteoporosis in 45 countries.)
The researchers found that the three medications reduce invasive breast cancer by 30 percent to 68 percent, depending on the drug. Tamoxifen and raloxifene were about the same in terms of reducing the risk of estrogen-receptor-positive breast cancer, which makes up about 60 percent of breast cancers. Health.com: Tips for staying hopeful If breast cancer spreads
However, the two drugs also increase the risk of blood clots, one of the most serious complications. (Clots can cause heart attacks and strokes).
Patients who took tamoxifen had a higher risk of cataracts and a greater chance of blood clots compared to those who took raloxifene. Women who took tamoxifen also had twice the risk of cancer of the endometrium, or uterine lining, as women who didn't take the drugs. Although doctors can monitor a woman for the early signs of endometrial cancer, she may need a hysterectomy to treat it.
Both tamoxifen and raloxifene cause hot flashes and other menopausal symptoms, according to the review. Tibolone was associated with a greater risk of stroke than other drugs, but the study authors say they need more data to truly determine its safety and effectiveness. Health.com: Fighting the cancer a mammogram can't catch
Russell recommends that women who are at high risk for breast cancer speak with their doctors and weigh the risks and benefits of drug therapy. High-risk women who have not yet entered menopause should consider tamoxifen; postmenopausal women should choose raloxifene due to its lower risk of certain side effects, she says.
The good news is that taking a SERM for about five years lowers a woman's risk even after she stops taking it. (Still, it doesn't guarantee that she won't get breast cancer.) The drugs prevent 7 to 10 cases of invasive breast cancer per 1,000 women per year of the drug's use. Health.com: Fighting the cancer a mammogram can't catch
So why aren't more women taking them? Russell says that explaining the risks and benefits of the drugs and managing and monitoring possible side effects can take time, a rare commodity for most doctors.
What's more, prevention of most conditions, whether breast cancer, diabetes, or heart disease, often takes a backseat to testing and treatment. "Physicians just are not rewarded for these types of preventive approaches," Russell says.
Women are considered to be at high risk for breast cancer based on several factors, including having close relatives with breast cancer (a mother, daughter, or sister) and being diagnosed with a precancerous breast condition. Health.com: Can Twitter and Facebook help fight breast cancer?
In general, women can lower their risk of breast cancer by maintaining a healthy body weight, exercising regularly, and limiting alcohol consumption, according to the American Cancer Society. Although regular mammograms don't prevent breast cancer, they can lead to earlier detection and more successful treatment.
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All About Breast Cancer