Drugs Can Cut Breast Cancer Risk for Some: Experts
Draft guidelines for doctors reflect findings, but it's hard to know who will benefit most, experts say
For both drugs, the benefits have to be weighed against the potential harms, Nelson said. "The tricky part is finding the right candidate" who is at increased risk of breast cancer and has a low risk of experiencing adverse events from the medications, she added.
The report looked at the rates of adverse events such as blood clots, which was about 90 percent more likely in studies of women taking tamoxifen and 60 percent more likely among women taking raloxifene. For tamoxifen, 8.6 per 1,000 women experienced a blood clot compared with 4.6 per 1,000 in the "control" group.
The rates of endometrial cancer, or cancer of the uterus, and cataracts were also higher for women taking tamoxifen, but not for those taking raloxifene, compared with their respective control groups.
In addition, "some women have side effects that are not life-threatening but they are uncomfortable and not minor, and cause them to stop medications, such as vaginal discharge, dryness, itching, leg cramps," Nelson explained.
Tamoxifen is currently approved by the U.S. Food and Drug Administration to reduce the risk of breast cancer among women at increased risk who are 35 years and older, whereas raloxifene is only approved for this use in postmenopausal women.
These medications are taken as a once-a-day pill and women are recommended to take them for five years, Nelson said. Raloxifene is also approved to prevent or treat osteoporosis, and for those uses women take the medication for a longer period of time, she noted.
Despite the fact that these medications have been available for a long time -- tamoxifen was approved for breast cancer chemoprevention in 1998 -- studies suggest they are underused. Only 60,000 women in the United States used tamoxifen in 2005, down from 120,000 in 2000, even though at least 2 million could be eligible for it.
Part of the problem could be that it is difficult for doctors to predict which patients are at high risk for developing breast cancer, Nelson explained. The FDA uses a risk assessment tool called the Gail model, which takes into consideration age, race, medical history and other factors, to define a woman's risk level, but even this model is not necessarily a good predictor for an individual patient, Nelson said.