Deciding Whether to Use Medicine to Reduce Breast Cancer Risk

If you are a woman who has a higher than average risk of breast cancer, you should know that drugs like tamoxifen and raloxifene  have been shown to help reduce the risk. Talk to a health care provider to find out if taking one of these drugs is an option for you.

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

Using drugs to help lower the risk of getting a disease is called chemoprevention. The first step in deciding if you should take a drug to help lower your chances of having 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.) All drugs have benefits and risks. For women with an increased risk of breast cancer, the benefits of chemoprevention may outweigh the risks.

For now, most experts say that your breast cancer risk should be higher than average for you to consider taking tamoxifen or raloxifene. If you do have a higher than average breast cancer 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 develop breast cancer. In fact, most women who have one or more risk factors will never develop breast cancer.

Risk factors for breast cancer include: 

  • Being a woman 
  • Getting older
  • Having blood relatives who had breast cancer
  • Your menstrual history
  • Your pregnancy history
  • Having had invasive breast cancer or ductal carcinoma in situ (DCIS) in the past
  • 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 family cancer syndrome (such as a BRCA mutation)

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 one of these. 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 was 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 are based largely on family history, such as the Tyrer-Cuzick model and the Claus model.

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

How high does my risk need to be?

Different studies have different definitions of a higher than average risk of breast cancer. Two big studies of tamoxifen and raloxifene, the Breast Cancer Prevention Trial (BCPT) and the Study of Tamoxifen and Raloxifene (STAR), used a 1.7% risk of developing breast cancer over the next 5 years as their cut-off point. (1.7% is the risk of a healthy woman aged 60.)

Some 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 only recommend chemoprevention for women 35 years and older with a 5-year risk of 3% or higher.

Most organizations recommend doctors and patients consider the use of either tamoxifen or raloxifene to lower risk. But at least one also recommends that doctors and their patients consider another type of drug called an aromatase inhibitor.

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 only women who are at a higher risk of breast cancer should take a drug to help lower their risk. 

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 and 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 in women who have gone through menopause.

You should talk with your doctor about your total health picture to make the best possible choice. 

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.

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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.

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Last Medical Review: June 1, 2016 Last Revised: August 18, 2016

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