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For women with a higher-than-average risk of breast cancer, some medicines can help reduce this risk. But these drugs can also have side effects, so it’s important to weigh their pros and cons before deciding to take one.

Chemoprevention

Taking medicines to help lower the risk of getting a disease is called chemoprevention.

The most commonly used medicines to lower breast cancer risk are tamoxifen and raloxifene. Other medicines called aromatase inhibitors (such as anastrozole and exemestane) might also be options.?

Should I take a drug to help reduce my breast cancer risk?

The first step in deciding if you should take a drug to help lower your chances of getting breast cancer is to have a health care provider assess your breast cancer risk.

Most experts say that your breast cancer risk should be higher than average for you to consider taking one of these drugs. If you do have a higher-than-average risk, you need to compare the benefit of possibly reducing your chance of getting breast cancer with the risk of side effects and other problems from taking one of these drugs.

Am I at higher risk for breast cancer?

A risk factor is anything that raises your risk of getting a disease. Your risk factors will need to be assessed to find out if you are at higher-than-average risk for breast cancer. But keep in mind that having risk factors does not mean that you will definitely develop breast cancer. In fact, most women who have one or more risk factors never develop breast cancer.

Some important risk factors for breast cancer include:

• Getting older
• Having close relatives who have had breast cancer
• Having a longer menstrual history (more total menstrual cycles)
• Having had invasive breast cancer or ductal carcinoma in situ (DCIS) before
• Being diagnosed with lobular carcinoma in situ (LCIS)
• Being diagnosed with atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH)
• Having a gene mutation linked to a family cancer syndrome (such as a BRCA mutation)

Some of these factors can increase your risk more than others.

How is breast cancer risk assessed?

Researchers have built some statistical models to help predict a woman’s risk of getting breast cancer.

For example, the (based on the modified Gail Model) is commonly used to assess risk. It can estimate your risk of getting breast cancer in the next 5 years and over your lifetime, based on many of the factors listed above.

This tool only looks at family history in close relatives (like siblings, parents, and children), though. And it can't be used to estimate risk if you have a history of ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), or breast cancer, or if you have a family cancer syndrome.

Also, the data that this tool is based on didn’t include American Indian or Alaskan Native women, so estimates for these women may not be accurate.

Other risk assessment tools, such as the Tyrer-Cuzick model and the Claus model, are based largely on family history. These tools? are used mainly by genetic counselors and other health care professionals.

These tools can give you a rough estimate of your risk, but no tool or test can tell for sure if you’ll develop breast cancer.

How high does my risk need to be?

There is no single definition of a higher-than-average risk of breast cancer. But most major studies have used a 1.7% risk of developing breast cancer over the next 5 years as their cut-off point. (This is the average risk for a 60-year-old woman.)

Some medical organizations recommend that doctors discuss the use of medicines to lower breast cancer risk in women at least 35 years old who have a 5-year risk of 1.7% or higher. Others might use different cutoff points.

The American Cancer Society does not have recommendations for using medicines to help lower the risk of breast cancer.

Are there reasons not to take one of these drugs to help reduce breast cancer risk?

All drugs have risks and side effects that must be discussed when making the decision about chemoprevention.

Most experts agree that tamoxifen and raloxifene should not be used to reduce breast cancer risk in women who:

• Have a higher risk of serious blood clots*
• Are pregnant or planning to become pregnant
• Are breastfeeding
• Are taking estrogen (including birth control pills or shots, or menopausal hormone therapy)
• Are taking an aromatase inhibitor
• Are younger than 35 years old

*Women who have a higher risk of serious blood clots include those who have ever had serious blood clots (deep venous thrombosis [DVT] or a pulmonary embolism [PE]). Many doctors also feel that if you’ve had a stroke or heart attack, or if you smoke, are obese, or have (or are being treated for) high blood pressure or diabetes, you also have a higher risk of serious blood clots. Women with any of these conditions should ask their doctors if the benefits of taking one of these drugs would outweigh the risks.

A woman who has been diagnosed with any type of uterine cancer or atypical hyperplasia of the uterus (a kind of pre-cancer) should not take tamoxifen to help lower breast cancer risk.

Raloxifene has not been tested in pre-menopausal women, so it should only be used if you have gone through menopause.

Aromatase inhibitors are not useful for pre-menopausal women, so they should only be used if you have gone through menopause. These drugs can cause bone thinning (osteoporosis), so they’re not likely to be a good option in women who already have thin or weakened bones.  

Talk with your doctor about your total health picture to make the best possible choice for you. 

To learn more about the use of these medicines for chemoprevention, see:

• Tamoxifen and Raloxifene for Lowering Breast Cancer Risk
• Aromatase Inhibitors for Lowering Breast Cancer Risk