Executive Summary
1. Researchers have found that some drugs indicated for breast cancer treatment—aromatase inhibitors (AIs) and selective estrogen receptor modulators (SERMs)—may also be effective for reducing the risk of developing breast cancer among high-risk women, with some studies showing upwards of a 50 percent decrease in cancer risk. The U.S. Food and Drug Administration (FDA) approved tamoxifen for this purpose years ago, and now raloxifene (a SERM) has also been approved. The AIs anastrozole, letrozole, and exemestane are not FDA-approved for preventive use. The AIs have only been studied in postmenopausal women, and are likely to be effective only in postmenopausal women.
2. SERMs block estrogen activity in certain tissues, whereas AIs block estrogen production in the adrenal glands and in fatty tissue. High-risk women who consider using these drugs for chemoprevention should take all of the potential side effects into account before starting a drug regimen, as they will need to be on the drug for years in most cases. Tamoxifen has a side effect of increasing the chances of developing endometrial cancer in postmenopausal women. Raloxifene and AIs do not carry that side effect but can only be used in postmenopausal women. Both SERMs can increase the risk of venous thrombosis and pulmonary emboli (blood clots that travel from the leg veins to the lungs), although raloxifene appears to be safer than tamoxifen for this problem. The AIs can lead to thinning of the bones (osteoporosis) and have undergone a shorter period of scrutiny for other side effects than SERMs.
3. Tamoxifen and the AIs have been shown to reduce recurrence of breast cancer among those who already have the disease, making them effective drugs for secondary chemoprevention. This indication has not yet been established for raloxifene.
4. Physicians should discuss breast cancer chemoprevention with all high-risk women. Women who are considering chemoprevention need to be aware of all of the potential benefits and risks and should carefully weigh those factors before making a decision. This requires a precise analytical tool to quantify, as accurately as possible, her real risk of developing breast cancer. Since those choosing chemoprevention will be healthy at the time of this decision and are expected to be taking the medication for a long period, the patient and her doctor must be fairly sure that she is a member of a significantly higher risk group before initiating this therapy.
5. Future research goals include the development of safer effective drugs, better risk models, and progress in preventing estrogen-receptor-negative tumors.
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