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Chemoprevention

If you are at high risk of breast cancer, you may be able to improve the chance of staying cancer-free by taking certain medications — this term is called chemoprevention.

There are two drugs that are approved by the FDA to be given for chemoprevention. Both of these drugs affect the hormone estrogen. The two drugs are called tamoxifen (Nolvadex) and raloxifene (Evista). These drugs belong to a class of drugs called Selective Estrogen Receptor Modulators (SERM). They will bind to both breast cancer cells and at-risk cells in place of estrogen, blocking the hormone’s effect and keeping those breast cells from dividing and growing.

Tamoxifen

This drug is used both to treat estrogen receptor positive breast cancer AND to decrease the risk of breast cancer in women who are at high risk. It is generally taken for five years. It is FDA approved in women who are age 35 and older and who have an elevated risk of developing breast cancer within five years. This is determined by a risk tool (Gail Model), breast biopsy results or genetic testing.

Data shows that tamoxifen can reduce your risk by as much as 50 percent. That sounds wonderful, but you must remember that it does not eliminate risk and the absolute numbers may not sound as good. Even high risk women do not always develop breast cancer, so some women are treated who will not get cancer. In other words, if you give 100 high risk women tamoxifen for five years, only two cases of breast cancer will be prevented. Whether tamoxifen might be right for you depends on your risk of breast cancer and the risk of the medication. Women who are at average to moderate risk are not recommended to take this medication.

Greatest benefit for those who

  • Are at high risk because of a personal or family history of breast cancer or because precancerous changes were found on a breast biopsy (ADH, LCIS)
  • Are premenopausal and have a low risk of developing blood clots or uterine cancer
  • Have had a hysterectomy

Common Side Effects

  • Hot flashes
  • Vaginal discharge
  • Vaginal dryness
  • Menstrual irregularities
  • Nausea

Tamoxifen can also cause rare, but potentially life-threatening side effects including blood clots, endometrial cancer and uterine cancer. Tamoxifen should never be used when a patient is pregnant or may become pregnant. A barrier contraception method must be used when a patient is taking this medication.

Raloxifene

This drug is also a SERM like tamoxifen, but it is only approved for risk reduction and is not used for the treatment of breast cancer (like tamoxifen). It is also approved as a treatment for osteoporosis. It may only be used in post-menopausal women.

A very large trial (The Study of Tamoxifen and Raloxifene — STAR) showed that raloxifene was as effective as tamoxifen in preventing breast cancer in high-risk postmenopausal women who did not have a history of breast cancer. This trial also showed less serious side effects with this drug — 29 percent fewer blood clots and 36 percent fewer uterine cancer.

Both drugs may cause hot flashes, bladder problems, vaginal discharge, vaginal dryness and irritation.

Women with a history of blood clots, cardiac risk factors, a prior history of coronary heart disease or who are at high risk of stroke should not take raloxifene or tamoxifen for prevention although the risk/benefit balance should be discussed with their physician. The decision must be individualized.