Deciding Whether to Use Medicine to Reduce Breast Cancer Risk

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 whether to take one.

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

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.

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. (See below for names of tools that can be used to do this.)

For now, 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.

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

Some important risk factors for breast cancer include: 

How is breast cancer risk assessed?

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

The Breast Cancer Risk Assessment Tool (also called the Gail Model) is commonly used to assess this 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.

The tool does have some limits, though. For instance, it only looks at family history in close relatives (like siblings, parents, and children). And it doesn’t estimate risk if you have a history of ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), or have had breast cancer. It’s also not helpful if you have a family cancer syndrome.

Also, the data that this tool is based on didn’t include Hispanic/Latina, 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 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. (1.7% is average risk of 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 the use of 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 neither tamoxifen nor raloxifene should 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 pulmonary embolism [PE]). Many doctors also feel that if you’ve had a stroke or heart attack you also have a higher risk of blood clots if you take these drugs. 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 these conditions should talk to their doctors to see if the benefits of chemoprevention 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, and should only be used if you have gone through menopause.

Aromatase inhibitors are not useful for pre-menopausal women, and 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. 

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Fisher B, Costantino JP, Wickerham DL, et al. Tamoxifen for the prevention of breast cancer: current status of the National Surgical Adjuvant Breast and Bowel Project P-1 study. J Natl Cancer Inst. 2005;97:1652–1662.

Moyer VM, on behalf of the US Preventive Services Task Force. Medications for Risk Reduction of Primary Breast Cancer in Women: US Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2013;159:698-708.

National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Breast Cancer Risk Reduction. V.1.2017. Accessed at www.nccn.org/professionals/physician_gls/pdf/breast_risk.pdf on August 9, 2017.

Visvanathan K, Hurley P, Bantug E, et al. Use of pharmacologic interventions for breast cancer risk reduction: American Society of Clinical Oncology clinical practice guideline. J Clin Oncol. 2013;31:2942-2962.

Vogel VG, Costantino JP, Wickerham DL, et al. Effects of tamoxifen vs raloxifene on the risk of developing invasive breast cancer and other disease outcomes: the NSABP Study of Tamoxifen and Raloxifene (STAR) P-2 trial. JAMA. 2006;295:2727–2741.

Vogel VG, Costantino JP, Wickerham DL, et al. Update of the National Surgical Adjuvant Breast and Bowel Project Study of Tamoxifen and Raloxifene (STAR) P-2 Trial: Preventing breast cancer. Cancer Prev Res (PhilaPa). 2010 Jun;3(6):696-706. Epub 2010 Apr 19.

Last Medical Review: September 6, 2017 Last Revised: September 6, 2017

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