Is There Medication to Prevent Breast Cancer?
Illustration by Julie Bang for Verywell Health
Fact checked by Nick Blackmer
Key Takeaways
England has approved a drug for breast cancer prevention—one that is also available in the U.S.
There are two main types of medications used to help prevent breast cancer in higher-risk patients: SERMs and AIs. These drugs work slightly differently but all help stop cancer cells from developing
Experts say it’s still important for people to go for regular breast cancer screenings and understand their individual risk based on factors such as family history.
England recently made headlines for approving the drug anastrozole for breast cancer prevention in women with an increased risk of developing the disease.
Anastrozole has been approved for years for breast cancer treatment, but the move by the healthcare system in England, National Health Service (NHS), to expand the drug’s use means that about 300,000 citizens who are at moderate or high risk for breast cancer can now benefit from it as a preventative tool.
The NHS said in a press release that while not all eligible candidates will choose to take the medication, it is estimated that if 25% do opt to take the drug, around 2,000 cases of breast cancer could potentially be prevented in the country.
While the news is celebrated in England, anastrozole has been used for both breast cancer treatment and prevention in the U.S. for many years. In fact, there are several drugs available for breast cancer prevention.
Here’s what you need to know about which drugs are available, how they work, and who is eligible.
Tamoxifen
What It’s Approved For
Tamoxifen belongs to a group of drugs called selective estrogen receptor modulators, or SERMs. These drugs can act as estrogen in the body or block against estrogen, depending on the target tissue.
Tamoxifen, also known by the brand name Soltamox, is used to treat hormone receptor-positive breast cancer, and it is also approved for breast cancer prevention in higher-risk patients.
Why It Helps Prevent Breast Cancer
“Tamoxifen is what we generally call an estrogen receptor blocker,” Nina D’Abreo, MD, director of medical oncology of the Perlmutter Cancer Center at NYU Langone Hospital, Brooklyn, told Verywell.
Because estrogen receptor-positive breast cancer is “fueled” by estrogen, the drug works by blocking estrogen in the breasts, as well as in other parts of the body. This essentially helps prevent cancer from growing in the breast.
How Effective Is It?
Clinical trials have found that tamoxifen can significantly reduce the likelihood of developing breast cancer.
One large National Cancer Institute-sponsored clinical trial found that in higher-risk postmenopausal patients, taking tamoxifen for five years reduced their risk of developing invasive breast cancer by about 50%.
The preventative effects last beyond the time a patient is on the medication, D’Abreo said, explaining that the reduced risk is long-lasting.
“The thing to remember is that you take the pills for five years, but this really is lifetime protection—it’s not just for the time you’re on the medication,” she said.
Who Is Eligible
The FDA has approved tamoxifen for patients with estrogen-positive breast cancer and people with a higher risk of developing the disease. Both premenopausal and postmenopausal patients are eligible to take this drug.
This high-risk group may include people with a family history of breast cancer, a history of lobular carcinoma in situ, a history of atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH) or a gene mutation linked to an increased chance of breast cancer, such as the BRCA mutation.
Patients can use an online tool to estimate their breast cancer risk through The Gail Model.
“Most of the studies [on breast cancer drugs] included women with a five-year risk of greater than 1.66 per cent based on The Gail model,” D’Abreo said.
It’s important to note, however, that The Gail Model does not accurately estimate breast cancer risk for patients with the BRCA1 or BRCA2 gene or a history of invasive or in situ breast cancer. There are also other factors the model cannot account for, so it’s crucial people speak to their healthcare provider to understand individual circumstances and prevention options.
How Do You Take It and What Are the Side Effects?
Tamoxifen is typically taken daily for five years for breast cancer prevention. It is available in both pill and liquid form.
D’Abreo said the side effects of tamoxifen tend to be well-managed and mild for most patients and can include hot flashes, weight gain, and vaginal dryness.
There are possible more serious side effects, like blood clots, uterine cancer, and stroke, but these tend to be very rare.
Related: How Younger Women Can Access Mammograms
Raloxifene
What It’s Approved For
Raloxifene, also known by the brand name Evista, is FDA-approved to reduce the risk of invasive breast cancer in postmenopausal patients. It is also used to prevent as well as treat osteoporosis in postmenopausal women. (Osteoporosis is the main use of the drug.)
It is not used as a treatment for breast cancer.
Why It Helps Prevent Breast Cancer
Raloxifene, like tamoxifen, is also a SERM.
“Raloxifene has only been studied in postmenopausal women, but it has a similar sort of mechanism as tamoxifen as it is an estrogen receptor blocker,” D’Abreo said.
The drug helps prevent breast cancer by blocking estrogen in the breast and other tissues. This is beneficial for patients with a higher risk of the disease because estrogen can support the growth of cancer cells.
How Effective Is It?
In a study comparing raloxifene and tamoxifen in patients over seven years (five years of taking the medication and two years of follow-up), researchers found that raloxifene can reduce risk of invasive breast cancer by about 38%.
Tamoxifen, on the other hand, showed about a 50% reduction rate over this period.
Who Is Eligible
Unlike tamoxifen, which can be used by both premenopausal and postmenopausal people, raloxifene is only approved for postmenopausal patients.
“The way it was studied initially was for prevention of bone loss,” Katherine Tkaczuk, MD, director of the Breast Evaluation and Treatment Program at the University of Maryland Greenebaum Comprehensive Cancer Center and a professor of medicine at the University of Maryland School of Medicine, told Verywell. “This drug is for older, postmenopausal women.”
A person using raloxifene for breast cancer prevention would need to be at a higher risk of developing the disease. These factors can include a family history of breast cancer or certain biopsy results, “such as finding lobular carcinoma in situ, atypical ductal hyperplasia or atypical lobular hyperplasia,” Tkaczuk said.
“If someone has these findings on their biopsy, this would automatically put them at higher risk,” she added.
Related: Menopause and Breast Cancer: What Is the Relationship?
How Do You Take It and What Are the Side Effects?
Raloxifene is an oral medication and it is taken daily, often for five years.
Common side effects include hot flashes, flu-like symptoms, abdominal pain, chest pain, joint pain, leg cramps, swelling of the legs and feet, cough, shortness of breath, and sweating.
Clinical trials found that the most serious adverse reaction related to the drug was venous thromboembolism (blood clotting in a vein).
D’Abreo said raloxifene has been used for a long time to treat osteoporosis, and that serious side effects, like blood clots, are very rare.
Anastrozole
What It’s Approved For
Anastrozole belongs to a class of drugs called aromatase inhibitors (AIs).
“Aromatase inhibitors work differently than SERMs, and they have also been used in the United States for [breast cancer treatment] for many years now,” D’Abreo said.
Anastrozole, which is sold under the brand name Arimidex, is FDA-approved for treatment of hormone receptor-positive breast cancer in postmenopausal patients. But it is also often used off-label for breast cancer prevention.
Another AI shown to help prevent breast cancer is exemestane (Aromasin). This drug is currently approved for the treatment of breast cancer but might be used off-label for prevention as well.
Why It Helps Prevent Breast Cancer
“This group of medications work by blocking the small amounts of estrogen that women make after menopause,” D’Abreo said.
In premenopausal patients, estrogen is produced mainly in the ovaries. It is also produced in peripheral tissues such as the breasts, liver, brain, skin, bone, and pancreas, though to a lesser degree.
But in patients who have gone through menopause, their ovaries are no longer making much estrogen, so peripheral tissues are the predominant source of the hormone.
Like SERMs, AIs target estrogen—but AIs work in the peripheral tissue, Tkaczuk said. AIs block the activity of an enzyme called aromatase, which the body uses to make estrogen. This blocking lowers the amount of estrogen made by the body, and in turn, can help prevent cancer cells from growing.
How Effective Is It?
Research on AIs shows about a 50% lifetime reduction risk of breast cancer when taken for five years, D’Abreo said.
In the NHS’s press release on approving anastrozole, the health agency said the drug “has been shown in trials to reduce the incidence of the disease in postmenopausal women at increased risk of the disease by almost 50%.”
It’s important to remember, however, that breast cancer prevention drugs are not for all types of breast cancer.
“Whether it’s SERM or an AI, such as anastrozole, they really only have been shown to prevent estrogen-positive breast cancer,” Tkaczuk said.
“They don’t really have much effect on certain more rare subtypes of breast cancer, such as triple-negative breast cancer.”
Who Is Eligible
This drug is only to be taken by postmenopausal patients. It is generally not to be used by premenopausal ones.
If the drug is used for breast cancer prevention, ideal candidates would be patients with higher risk of developing breast cancer.
Like with the SERMs, high-risk factors can include a history of breast cancer in the family, abnormal breast cell growth or biopsy results, and an elevated score of breast cancer risk on The Gail Model.
How Do You Take It and What Are the Side Effects?
The side effects of AIs are similar to menopause, D’Abreo said. They can include hot flashes, joint stiffness, vaginal dryness, insomnia and hair thinning.
“The side effect that’s most important for us is the bone loss that happens—osteopenia or osteoporosis,” D’Abreo said.
Research shows that female patients taking an AI are at a two- and four-fold increased risk of bone loss compared to females in the general population. This differs from a SERM like raloxifene which helps prevent bone loss.
“If you have bone loss already from natural menopause, these AIs can increase the risk of bone loss while you're on the pill,” D’Abreo said.
The Importance of Screening
While breast cancer prevention medications are incredibly helpful in reducing the likelihood of developing the disease, experts say regular screenings—including check-ups and mammograms—are vital. Speaking with your healthcare provider about your breast cancer risk can help prevent disease or disease progression.
Related: At What Age Should You Get a Mammogram?
“Even if you don’t have a biopsy that shows one of the high-risk findings, speak to your [healthcare provider] to see whether you would be somebody who could be considered a higher risk for breast cancer,” D’Abreo said.
What This Means For You
England recently made headlines for approving the drug anastrozole for breast cancer prevention in women with an increased risk of developing the disease. The drug has been used for breast cancer prevention in the U.S. for years, and is one of several available medications.
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