At High Risk for Breast Cancer? Chemoprevention May Be for You

About 1 in 8 women in the U.S. will develop breast cancer in their lifetime. In fact, it’s the second leading cause of cancer-related death in this group. But did you know that some people have the option of taking medication to lower their breast cancer risk?

Breast cancer chemoprevention is when you take medications to lower the likelihood of developing cancer. It’s been shown to lower breast cancer risk by up to 65% in people at high risk of having breast cancer. About 10 million people in the U.S. are eligible for chemoprevention. Yet some estimate that less than 5% of high-risk people end up taking it. 

Here we’ll discuss what you should know about breast cancer chemoprevention — what it is, how it works, and whether it’s right for you.

What is breast cancer chemoprevention?

Some people have a higher risk of developing breast cancer. This includes people with specific genetic factors or a family history of breast cancer. 

Breast cancer chemoprevention is when a healthy person takes medications to lower their cancer risk. This may help people who have a higher risk of developing breast cancer. But some people who’ve already had cancer may also use chemoprevention to try to stop it from coming back. But chemoprevention isn’t for everyone. There are side effects and risks that might not outweigh the benefits.

That’s why your healthcare provider can help you estimate your breast cancer risk. If your risk is higher than average, chemoprevention might be an option.

Who can get breast cancer chemoprevention?

First, let’s review risk factors that may raise breast cancer risk. There are lifestyle factors, like drinking alcohol and using hormonal medications (e.g., birth control), that may raise your risk.

But there are also other factors that you can’t control. Examples of these risk factors include:

• Being a woman

• Older age

• Personal or family history of breast cancer

• Gene changes from your parents (e.g., BRCA mutation)

• Race and ethnicity

• Starting monthly bleeding before age 12

• Starting menopause after age 55

• Prior radiation to your chest, especially as a teen or young adult

• History of certain non-cancerous breast conditions

Having a risk factor doesn’t mean you’ll get breast cancer. It also doesn’t mean you should take chemoprevention. There are different calculators that use personal information to estimate breast cancer risk. 

Common risk assessment tools include:

• Breast Cancer Risk Assessment Tool: This tool is also called the Gail Model. It estimates the risk of getting breast cancer within the next 5 years and over your lifetime. It’s a common tool, but it may not be the best for everyone. For example, it may not be as accurate for American Indian or Alaska Native populations.

• IBIS Breast Cancer Risk Evaluation Tool: This tool estimates breast cancer risk within the next 10 years and over your lifetime. It may be helpful for people with lobular carcinoma in situ (LCIS). LCIS is a condition where abnormal cells form in the milk glands.

• Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm: This tool estimates breast cancer risk based on family history. It’s also a tool for people with a BRCA gene mutation.

We know that risk for breast cancer can vary by race. Some tools have varying levels of accuracy for African American and Asian American and Pacific Islander (AAPI) populations.  

Talk to your healthcare provider about your risks to see which calculator would be the best for you. Your age and calculator score can help your provider decide if you’d benefit from chemoprevention.

Who shouldn’t take chemoprevention for breast cancer?

Like all medications, chemoprevention medications can have side effects. These side effects may not be safe for everyone. Because of this, experts agree that you should avoid these medications if you:

• Are under age 35

• Have a high risk of serious blood clots or stroke

• Are pregnant or planning to become pregnant

• Are nursing

• Are taking medications that have estrogen (e.g., birth control)

• Were diagnosed with uterine cancer or another type of precancer of the uterus

Every person is different. There may be other situations that may not make chemoprevention the best option for you. That’s why it’s important to discuss risks and benefits with your healthcare provider.

What medications are used for breast cancer prevention?

If chemoprevention is right for you, there are two types of medications you may use. These include selective estrogen receptor modulators (SERMs) and aromatase inhibitors. They generally work by lowering estrogen levels. Estrogen is like a fuel source that helps cancer grow.

Experts agree that the benefits of these medications are greater than the risks for certain people. This includes women who are at least 35 years old with a higher risk of breast cancer. As mentioned above, these medications can lower breast cancer risk by up to 65%.

Selective estrogen receptor modulators

SERMs lower the risk of breast cancer by blocking the effects of estrogen in breast tissue. But even though they block estrogen’s effects in breast tissue, they can act like estrogen in other parts of your body. They’re taken for at least 5 years for chemoprevention. Examples include tamoxifen and raloxifene (Evista). 

There are a few common side effects and risks with SERMs, including:

• Menopause symptoms: SERMs can cause mood changes, night sweats, and hot flashes similar to those you may experience during menopause. You may have monthly bleeding changes and vaginal dryness and discharge. In some cases, your monthly bleeding might stop completely and not return.

• Blood clots: These medications can raise the risk of blood clots in veins. This can happen in your legs or lungs and can be dangerous. This is why people at high risk for blood clots shouldn’t take these medications.

• Uterine cancers: Tamoxifen (but not raloxifene) can act like estrogen in the uterus. Although rare, it can raise your risk for developing cancer in the uterus. 

Tamoxifen

Tamoxifen can be used for chemoprevention and breast cancer treatment. A study of over 13,000 women found that tamoxifen lowered the risk of breast cancer by about 50%.

Tamoxifen is available as a lower-cost generic oral tablet. You’ll typically take 20 mg by mouth every day for 5 years for chemoprevention. You may take it before or after menopause. 

Besides the side effects listed above, there are a few unique to tamoxifen: 

• Osteoporosis: Tamoxifen has bone-protecting effects because it acts like estrogen in bone. This is why it’s sometimes used to prevent osteoporosis (when bones become weak and break easily). But this benefit only applies to people who’ve been through menopause. If you haven’t gone through menopause yet, tamoxifen may cause bone loss.

• Eye problems: Tamoxifen has been linked to eye problems. One study found that tamoxifen raised the risk of cataracts (when your eye lens becomes cloudy). This risk goes up the longer you take tamoxifen.

Raloxifene

Raloxifene (Evista) can be used to lower the risk of breast cancer after menopause. It can also be used to treat and prevent osteoporosis after menopause. 

Long-term studies have found that it isn’t as effective as tamoxifen for chemoprevention once you stop taking it. But it can still be a good option if you want to avoid certain side effects from tamoxifen.

Raloxifene is available as a lower cost generic oral tablet. You’ll typically take 60 mg by mouth every day for 5 years for chemoprevention. But you may stay on it longer if you’re taking it for osteoporosis.

Aromatase inhibitors

Aromatase inhibitors work by stopping an enzyme (protein) in fat tissue called aromatase. Aromatase turns other hormones (like testosterone) into estrogen. Blocking aromatase lowers the amount of estrogen in your body. 

Aromatase inhibitors are taken daily for at least 5 years for chemoprevention. Examples include anastrozole (Arimidex) and exemestane (Aromasin). Unlike SERMs, aromatase inhibitors aren’t FDA approved for chemoprevention. Instead, they’re used off-label — in a way that hasn’t been approved by the FDA.

These medications don’t stop your ovaries from making estrogen. As mentioned, they work in fat cells outside of your ovaries. That’s why they’re mainly recommended for people who’ve gone through menopause. This is because after menopause, most of your estrogen comes from fat tissue instead of your ovaries.

Common side effects and risks with aromatase inhibitors include:

• Menopause symptoms: Like SERMs, these medications can cause hot flashes and vaginal dryness. This is because they also lower estrogen in your body.

• Muscle and joint pain: Aromatase inhibitors can cause muscle and joint pain, mostly in the hands, knees, and back. This usually happens around 2 months after starting treatment.

• Osteoporosis: Lower estrogen levels can affect bone density. This leads to weaker bones and a greater risk for fracture (break). This risk is highest during the first 2 years of treatment. But it’s possible for bone density to improve after stopping the medication. And there are medications that can help prevent or treat this side effect, too.

• Cardiovascular disease: People with certain types of heart disease may be at risk for heart problems like heart attacks. Aromatase inhibitors can elevate cholesterol (fats in the blood), raising your risk for heart problems.

Anastrozole

Anastrozole (Arimidex) is a tablet that you take by mouth. For chemoprevention, your provider may suggest you take 1 mg by mouth once a day for 5 years. One study found that anastrozole lowered the risk of breast cancer by about 49%.

Exemestane

Exemestane (Aromasin) is also a tablet you take by mouth. Your provider may suggest you take 25 mg by mouth once a day after a meal. It’s taken for 5 years to lower the risk of breast cancer. In one trial, exemestane lowered the risk of breast cancer by 65%.

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Written by:

Emmeline C. Academia, PharmD, BCOP

Emmeline C. Academia, PharmD, BCOP, has been a practicing clinical pharmacist in adult oncology since 2020. She is a clinical pharmacy specialist in oncology at Beth Israel Deaconess Medical Center, in Boston.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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