Chemoprevention is the use of drugs to lower the risk of breast cancer in women at higher risk. Tamoxifen and raloxifene are the only two drugs FDA-approved for breast cancer chemoprevention.
Tamoxifen and raloxifene
Both tamoxifen and the osteoporosis drug raloxifene can lower the risk of breast cancer by about half in women at higher risk [217-222]. Tamoxifen and raloxifene only reduce the risk of estrogen receptor-positive cancers. Neither drug reduces the risk of estrogen receptor-negative cancers [222]. Although tamoxifen and raloxifene give a similar prevention benefit, there are some differences between the two. These are listed in the table below.
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Tamoxifen
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Raloxifene
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Who can take the drug?
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Premenopausal and postmenopausal women
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Postmenopausal women only
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How is high-risk defined?
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Women at least 35 years of age with a 5-year risk of breast cancer of 1.67% or more according to the Breast Cancer Risk Assessment Tool (Gail model).
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Women with any one of:
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What are the breast cancer prevention benefits?
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Lowers the risk of invasive and non-invasive breast cancers, such as ductal carcinoma in situ (DCIS).
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Lowers the risk of invasive breast cancers, but not non-invasive breast cancers.
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What are the long-term side effects?
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Modestly increases the risk of:
- Stroke
- Blood clots in the large veins (deep venous thrombosis)
- Blood clots in the lungs (pulmonary emboli)
- Cataracts
- Cancer of the uterus
Side effects occur mainly in older postmenopausal women.
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Modestly increases the risk of:
- Stroke
- Blood clots in the large veins (deep venous thrombosis)
- Blood clots in the lungs (pulmonary emboli)
Side effects occur mainly in older postmenopausal women.
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| What are the short-term side effects? |
- Hot flashes
- Vaginal discharge
Other side effects are rare.
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- Hot flashes
- Leg cramps
- Swelling in the legs, hands or feet
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What about use in treatment?
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Effective in the treatment of hormone receptor-positive breast cancer (see Treatment chapter).
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Has not been shown to be effective for the treatment of breast cancer.
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Adapted from Kinsinger LS et al., Cuzick J et al. and Fisher B et al. [217,223,224].
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Tamoxifen and raloxifene also have some long-term side effects (see table above) and may not be suitable for all women at higher risk. Talk to your health care provider about the potential harms and benefits of these drugs. For more on talking to your provider, visit the Getting Good Care section.
Tamoxifen and anti-depressants
Certain types of anti-depressants called selective serotonin reuptake inhibitors (SSRIs) can interfere with the metabolism of tamoxifen (how tamoxifen works in the body) [225]. If you are taking SSRIs to treat depression or menopausal symptoms, talk to your health care provider about possible drug interactions and other options for treating symptoms.
BRCA mutations and tamoxifen
Researchers are assessing whether tamoxifen also lowers the risk of breast cancer in women who have a BRCA1 or BRCA2 mutation [202,226,227]. Some studies have suggested that tamoxifen may be less effective in preventing breast cancer in BRCA1 carriers [228]. These women are less likely to have tumors with estrogen receptors and tamoxifen works by attaching to these receptors. Thus, it may be less effective in reducing the risk of these cancers.
Although one study suggested that tamoxifen could lower breast cancer risk in healthy BRCA2 carriers, that study was too small to be conclusive [227]. However, some findings have shown that tamoxifen might offer benefit to BRCA1 and BRCA2 carriers who have been diagnosed with breast cancer in the past [226,229]. The risk of breast cancer in the unaffected breast may be reduced by as much as 75 percent with two to four years of tamoxifen use [226].
Ethnicity and tamoxifen
At this time, there are few data on the potential benefits and harms of tamoxifen for African American women and women of other ethnicities. It’s likely, however, that African American women get less benefit and more harm from tamoxifen than white women. African Americans have a lower rate of breast cancer than whites and are also more likely to suffer some of the harmful side effects of tamoxifen.
Other risk-lowering drugs
New risk-lowering drugs are being developed and some drugs used for breast cancer treatment are under study for their use in prevention. For example, the hormone drugs called aromatase inhibitors are being tested in postmenopausal women. Before joining a clinical trial of risk-lowering drugs, however, you should discuss the potential risks and benefits with your health care provider. For more information on clinical trials, see the Treatment section.
Updated 11/10/09
