It has been used for many years to reduce the risk of recurrence in localized breast cancer and as a treatment for advanced breast cancer when the tumor is estrogen-receptor positive (see the section, "How is breast cancer treated?"). Several studies have found that tamoxifen can also lower the risk of getting breast cancer in women who are at increased risk for the disease.
Results from the Breast Cancer Prevention Trial (BCPT) have shown that women at increased risk for breast cancer are less likely to develop the disease if they take tamoxifen. Women in the study took either tamoxifen or a placebo pill for 5 years. After 7 years of follow-up, women taking tamoxifen had 42% fewer breast cancers than women who took the placebo, although there was no difference in the risk of dying from breast cancer.
Tamoxifen is approved by the US Food and Drug Administration (FDA) for reducing breast cancer risk in women at high risk. Tamoxifen has side effects that include increased risks of endometrial (uterine) cancer and blood clotting, so women should consider the possible benefits and risks of tamoxifen before deciding if it is right for them.
And while tamoxifen seems to reduce breast cancer risk in women with BRCA2 genemutations, the same may not be true for those with BRCA1 mutations. Raloxifene: Like tamoxifen, raloxifene also blocks the effect of estrogen on breast tissue.
A study comparing the effectiveness of the 2 drugs in women after menopause, called the Study of Tamoxifen and Raloxifene (STAR) trial, found that raloxifene worked nearly as well as tamoxifen in reducing the risk of invasive breast cancer and non-invasive cancer (DCIS or LCIS). Raloxifene also had lower risks of certain side effects such as uterine cancer and blood clots in the legs or lungs, compared to tamoxifen (although the risk of blood clots was still higher than normal).
Raloxifene is FDA approved to help reduce breast cancer risk in women past menopause who have osteoporosis (bone thinning) or are at high risk for breast cancer. Aromatase inhibitors: Drugs such as anastrozole, letrozole, and exemestane are also being studied as breast cancer chemopreventive agents in post-menopausal women.
These drugs are already being used to help prevent breast cancer recurrences. They work by blocking the production of small amounts of estrogen that post-menopausal women normally make. A recent study showed exemestane can lower the risk of invasive breast cancer by 65% in post-menopausal women who have an increased risk for breast cancer. But they can also have side effects, such as causing joint pain and stiffness and bone loss, leading to a higher risk of osteoporosis. None of these drugs is currently FDA-approved for reducing the risk of developing breast cancer.
Other drugs : Studies are looking at other drugs as well. For example, some studies have found that women who take aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen seem to have a lower risk of breast cancer. Studies are also looking to see if drugs called bisphosphonates may lower the risk of breast cancer. Bisphosphonates are drugs that are mainly used to treat osteoporosis, but they are also used to treat breast cancer that has spread to the bone. These, as well as several other drugs and dietary
supplements, are being studied to see if they can lower breast cancer risk, but none is approved for reducing breast cancer risk at this time.
Many of the drugs mentioned here are discussed further in the section, "How is breast cancer treated?" For more information on the possible benefits and risks of chemopreventive drugs see our document, Medicines to Reduce Breast Cancer Risk.
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