The Who, What, Where, When and Sometimes, Why.

Aromatase Inhibitors

Aromatase inhibitors are a hormone therapy (also called endocrine therapy). They are used to treat hormone receptor-positive early, locally advanced and metastatic breast cancers.

Learn about aromatase inhibitors and other hormone therapies for metastatic breast cancer.

How do aromatase inhibitors work?

Hormone receptor-positive breast cancers need estrogen and/or progesterone (female hormones) to grow.

Aromatase inhibitors lower estrogen levels in the body by blocking aromatase, an enzyme that converts other hormones into estrogen. This slows or stops the growth of the tumor by preventing the cancer cells from getting the hormones they need to grow.

Aromatase inhibitors include:

  • Anastrozole (Arimidex)
  • Exemestane (Aromasin)
  • Letrozole (Femara)

To learn about a specific aromatase inhibitor, visit the National Institutes of Health’s Medline Plus website.

Aromatase inhibitors as breast cancer treatment

For women with hormone receptor-positive breast cancer, treatment with an aromatase inhibitor (alone or after several years of tamoxifen) lowers the risk of [79]:

Among postmenopausal women with hormone receptor-positive breast cancer, aromatase inhibitors (alone or after tamoxifen) offer the same or slightly greater benefit compared to tamoxifen alone [79,90-93].

Anastrozole, exemestane and letrozole are equally effective and have similar side effects [79,90-93]. However, you may tolerate one drug better than another.  

 

For a summary of research studies on aromatase inhibitors and early breast cancer, visit the Breast Cancer Research Studies section.

Who can take aromatase inhibitors?

Aromatase inhibitors are used to treat breast cancer in women. They are not used to treat breast cancer in men.

Menopausal status

In general, aromatase inhibitors are only used to treat breast cancer in postmenopausal women.

However, some premenopausal women may take an aromatase inhibitor when combined with ovarian suppression.

Ovarian suppression prevents the ovaries from making estrogen, so a woman becomes postmenopausal. Ovarian suppression is usually done with drug therapy so menopause is temporary.

How are aromatase inhibitors taken?

Aromatase inhibitors are pills. You take one pill every day.

Postmenopausal women with hormone receptor-positive breast cancer can:

  • Begin hormone therapy with an aromatase inhibitor 
  • Begin hormone therapy with tamoxifen and then after a few years, switch to an aromatase inhibitor

When an aromatase inhibitor is the only hormone therapy given, it’s taken for 5-10 years.

When an aromatase inhibitor is taken after tamoxifen, the drugs are taken for a combined total of 5-10 years.

Talk with your health care provider about how long you should take an aromatase inhibitor.

Find a list of questions on hormone therapy for your health care provider.

Length of treatment with an aromatase inhibitor

Randomized clinical trials have compared outcomes for women who used aromatase inhibitors for 10 years versus 5 years [94]. Taking an aromatase inhibitor for 10 years [94]:

  • Improves disease-free survival
  • Lowers the risk of cancer in the opposite breast (contralateral breast cancer)

However, overall survival is the same whether a woman takes an aromatase inhibitor for 5 years or 10 years [94]. For most women, the benefit of the extra 5 years of treatment is small [94].

Women who take an aromatase inhibitor for more than 5 years continue to have side effects from the drug, including a higher number of bone fractures and a higher rate of osteoporosis [94-96].

Talk with your health care provider about how long you should take an aromatase inhibitor.

Learn about the importance of completing treatment with an aromatase inhibitor.

Possible side effects of aromatase inhibitors include muscle pain, joint pain and menopausal symptoms (such as hot flashes).

Aromatase inhibitors also cause a loss of bone density. Women who take an aromatase inhibitor get a baseline measure of their bone density so changes to bone density can be monitored.

Learn more about the side effects of aromatase inhibitors.

Aromatase inhibitors don’t normally work in premenopausal women because their ovaries are still making estrogen.

However, some premenopausal women may take an aromatase inhibitor when combined with ovarian suppression, which shuts down the ovaries.

Learn more about ovarian suppression and aromatase inhibitors.

Aromatase inhibitors and risk reduction

Aromatase inhibitors have been studied in the risk reduction setting.

Findings from randomized controlled trials have shown the aromatase inhibitors exemestane and anastrozole may lower the risk of developing breast cancer in postmenopausal women at high risk [97-98].

However, aromatase inhibitors are not FDA-approved for use as risk-lowering drugs.

Learn more about risk-lowering drugs for women at high risk of breast cancer.

Importance of following your breast cancer treatment plan

Breast cancer treatment is most effective when all parts of the treatment plan are followed as prescribed.

It’s important to follow the treatment plan (for medications and other therapies) prescribed by your health care provider in terms of:

  • Timing
  • Dose
  • Frequency

Completing aromatase inhibitor therapy

Aromatase inhibitors are prescribed for 5-10 years. The length of this treatment along with side effects can make it tough to complete treatment.

Dealing with menopausal symptoms related to hormone therapy can be hard. Talk with your health care provider about ways to ease these and other side effects.

To get the most benefit out of hormone therapy, you need the full course of treatment. Women who complete the full course have better survival than those who don’t [82-84].

If you have trouble remembering to take your medicine, a pillbox or setting an alarm on your watch or phone (you may be able to download an app) may help [1].

However, you don’t need to panic if you miss a day or two.

Learn more about the importance of following your breast cancer treatment plan.

Learn about ways to manage hot flashes and other menopausal symptoms.

Prescription drug assistance

Hormone therapy drug costs can quickly become a financial burden for you and your family.

Medicare and many insurance companies offer prescription drug plans. One may already be included in your policy or you may be able to buy an extra plan for prescriptions.

Aromatase inhibitors are pills, so they’re covered under your health insurance plan’s prescription drug benefit rather than the plan’s medical benefit. This means there are usually out-of-pocket costs, which can add up over time.

You may qualify for programs that help with drug costs or offer low-cost or free prescriptions.

Anastrozole, exemestane and letrozole all have generic forms. Generics cost less than name brand drugs, but are just as effective.

Learn more about insurance plans and prescription drug assistance programs.  

Learn about other financial assistance programs.

 Susan G. Komen®’s position on fairness in oral cancer drug coverage

Insurance coverage of oral cancer drugs

Cancer medications given by vein (through an IV) are usually covered under a health insurance plan’s medical benefit. However, cancer medications that are pills (oral cancer drugs) are usually covered under a health insurance plan’s prescription drug.

As a result, people often find themselves facing high out-of-pocket costs when filling prescriptions for oral cancer drugs. Sometimes this can cost thousands of dollars a month.

The impact of high drug costs

High prescription drug costs are a barrier to care. They can prevent people from getting the medications prescribed by their health care providers.

No one should be forced to get less appropriate treatment because an insurer gives more coverage for IV drugs than pills.

Efforts to increase fairness in drug coverage

Komen supports state and federal efforts to require insurers to provide the same or better coverage for oral cancer drugs as they do for IV cancer drugs. This would help ensure patients have access to affordable, appropriate treatment.

Take action

Ask your U.S. representative to co-sponsor the Cancer Drug Parity Act.

Komen Treatment Assistance Program

Susan G. Komen® offers the Komen Treatment Assistance Program to help eligible, underserved breast cancer patients in treatment. To learn more about this program and other helpful resources, call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636).

 SUSAN G. KOMEN® SUPPORT RESOURCES 

 
  • If you or a loved one needs more information about breast health or breast cancer, call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636). All calls are answered by a trained specialist or oncology social worker in English and Spanish, Monday through Friday from 9:00 a.m. to 10:00 p.m. ET. You can also email the helpline at helpline@komen.org
  • We offer an online support community through our closed Facebook Group – Komen Breast Cancer group. The Facebook group provides a place where those with a connection to breast cancer can discuss each other’s experiences and build strong relationships to provide support to each other. Visit Facebook and search for “Komen Breast Cancer group” to request to join the closed group.
  • Komen Affiliates offer breast health education and some fund breast cancer programs through local community organizations. Your local Affiliate may also help you find breast cancer resources in your area. Find your local Affiliate. 
  • Our Family and Friends section has detailed information and resources for loved ones.
  • Our fact sheets, booklets and other education materials offer additional information.