Breast cancer chemoprevention: Medicines that reduce breast cancer risk

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Breast cancer chemoprevention: Medicines that reduce breast cancer risk

Preventive medications (chemoprevention) reduce breast cancer risk for women at high risk of developing the disease. Find out how these medications work plus associated side effects and health risks.
By Mayo Clinic staff

If you're at high risk of breast cancer, you may be able to improve your odds of staying cancer-free by taking certain medicines, an approach known as chemoprevention or chemoprophylaxis.

The best-known options are selective estrogen receptor modulators (SERMs) — tamoxifen and raloxifene (Evista). Both drugs have Food and Drug Administration (FDA) approval for the prevention of breast cancer in high-risk women.

Research continues to explore the breast cancer prevention potential of tamoxifen, raloxifene and several new medications, and recommendations for their use undoubtedly will change.

Tamoxifen
How it works
Tamoxifen blocks the effects of estrogen, a reproductive hormone that influences the growth and development of many breast tumors. Tamoxifen is usually prescribed as a pill you take once a day by mouth. For breast cancer prevention, tamoxifen is typically taken for a total of five years.

Who it's for
Tamoxifen is FDA approved for breast cancer prevention in high-risk women age 35 and older, whether or not they've gone through menopause. Generally speaking, you might consider chemoprevention with tamoxifen if:

Your Gail model risk score is greater than 1.66 percent. The Gail model is a tool doctors use to predict future risk of developing breast cancer based on factors such as your age, reproductive history and family history.
You're at high risk of developing breast cancer — for instance, you've been diagnosed with a precancerous condition such as atypical hyperplasia or lobular carcinoma in situ (LCIS).
You have a strong family history of breast cancer.
You don't have a history of blood clots.
You've had a hysterectomy.
Common side effects
Common side effects of tamoxifen include:

Hot flashes
Vaginal discharge
Vaginal dryness
Menstrual irregularities
Bladder or urinary problems
Nausea
Risks
Rarely, taking tamoxifen may cause:

Blood clots
Endometrial cancer or uterine cancer
Cataracts
Stroke
Taking tamoxifen doesn't guarantee that you'll remain cancer-free. Unless you're at high risk of developing breast cancer, the potential risks of tamoxifen may outweigh the benefits for you.

Raloxifene
How it works
Raloxifene is also prescribed in pill form, to be taken by mouth once a day. Like tamoxifen, raloxifene works by blocking estrogen's effects in the breast and other tissues. Unlike tamoxifen, raloxifene doesn't exert estrogen-like effects on the uterus.

Who it's for
Raloxifene is currently approved by the FDA for reducing breast cancer risk in high-risk women who are past menopause (postmenopausal). You're considered at high risk if you score greater than 1.66 percent on the Gail model. Raloxifene is also approved for prevention and treatment of the bone-thinning disease osteoporosis in postmenopausal women.

Common side effects
Common side effects of raloxifene include:

Hot flashes
Vaginal discharge
Vaginal dryness or irritation
Bladder or urinary problems
Joint and muscle pain
Weight gain
Risks
Health risks associated with raloxifene are similar to those associated with tamoxifen. Both drugs carry an increased risk of blood clots. However, raloxifene may be associated with fewer cases of endometrial and uterine cancers than is tamoxifen. Raloxifene may also be linked to fewer strokes than tamoxifen in women at average risk of heart disease. But if you have heart disease or you have multiple risk factors for heart disease, such as high cholesterol, high blood pressure and obesity, raloxifene may actually increase your risk of strokes.

Breast cancer chemoprevention: Medicines that reduce breast cancer risk
Aromatase inhibitors
Aromatase inhibitors aren't FDA approved for breast cancer chemoprevention, but they are the subject of much ongoing research.

How they work
Aromatase inhibitors are a class of medicines that reduce the amount of estrogen in your body, depriving breast cancer cells of the fuel they need to grow and thrive. Three aromatase inhibitors are currently used in the treatment of women with breast cancer: anastrozole (Arimidex), exemestane (Aromasin) and letrozole (Femara). These medications are used after breast cancer surgery to prevent breast cancer from returning (recurring).

Who they're for
Aromatase inhibitors have been studied and shown to be effective in postmenopausal women to treat breast cancer and to prevent breast cancer recurrence. Aromatase inhibitors are not intended for preventing breast cancer recurrence in women who still have menstrual cycles.

Common side effects
Common side effects of aromatase inhibitors include:

Hot flashes
Vaginal dryness
Joint and muscle pain
Headache
Risks
Aromatase inhibitors raise the risk of:

Broken bones (fractures)
Osteoporosis
Because aromatase inhibitors are a newer class of medications, not much is yet known about long-term health risks, such as heart disease. As more results from research studies become available, doctors will have a better idea of these long-term health implications, as well as of the drugs’ effectiveness in breast cancer chemoprevention.

A word about aspirin
Several studies have looked into the effects of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) on breast cancer risk. NSAIDs include many common over-the-counter painkillers, such as ibuprofen (Advil, Motrin, others) and naproxen sodium (Aleve).

Study results are mixed. Some research has found that women who had breast cancer and who regularly take aspirin or other NSAIDs have a slightly decreased risk of breast cancer recurrence. But other studies haven't shown a significant association between breast cancer risk and NSAIDs.

It remains unknown whether aspirin and other NSAIDs help protect against breast cancer, and if so, exactly how they work to do so. Because some NSAIDs, such as celecoxib (Celebrex) and naproxen sodium (Aleve), may increase the risk of heart attack and stroke, talk with your doctor to weigh the potential benefits versus the risks of taking an NSAID in your situation.

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