Hormone receptor-positive breast cancers need estrogen and/or progesterone (female hormones that are produced in the body) to grow.
Aromatase inhibitors are hormone therapy drugs that can slow or stop the growth of hormone receptor-positive tumors. They lower estrogen levels in the body by blocking aromatase, an enzyme that converts other hormones into estrogen. This prevents the cancer cells from getting the hormones they need to grow.
Aromatase inhibitors include:
To learn about a specific aromatase inhibitor, visit the National Institutes of Health's Medline Plus website.
For women with hormone receptor-positive breast cancer, treatment with an aromatase inhibitor (alone or after several years of tamoxifen) lowers the risk of :
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 [62,69-71].
Anastrozole, exemestane and letrozole are equally effective and have similar side effects [62,69-71].
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.
Aromatase inhibitors are used to treat hormone receptor-positive early and metastatic breast cancers.
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.
Women with certain heart problems should not take anastrozole.
Aromatase inhibitors come in pill form. You take one pill every day.
Postmenopausal women with hormone receptor-positive breast cancer can:
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.
A recent randomized clinical trial compared 10 years of use of the aromatase inhibitor letrozole to 5 years of use .
Women who used letrozole for 10 years had :
However, overall survival was the same whether a woman took the aromatase inhibitor for 5 years or 10 years . And, women who took letrozole for 10 years continued to have side effects from the drug, including a higher number of bone fractures and a higher rate of osteoporosis .
Talk with your health care provider about the best length of time for you to take an aromatase inhibitor.
The side effects of aromatase inhibitors include muscle and 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 that changes to bone density can be monitored.)
Learn more about the side effects of aromatase inhibitors.
Aromatase inhibitors do not usually work in premenopausal women because their ovaries are still making estrogen.
But, because ovarian suppression shuts down the ovaries, some premenopausal women may take an aromatase inhibitor when combined with ovarian suppression.
Learn more about ovarian suppression and aromatase inhibitors.
Aromatase inhibitors are also being studied in the chemoprevention (risk-lowering drugs) 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 [72-73].
However, aromatase inhibitors do not yet have FDA-approval for use in the risk reduction setting.
Learn more about risk-lowering drugs for women at high risk of breast cancer.
Breast cancer treatment is most effective when all parts of the treatment plan are followed.
It is important to follow the treatment plan (for medications and other therapies) prescribed by your health care provider in terms of:
Because aromatase inhibitors are prescribed for 5-10 years, the length of this treatment coupled with side effects can make it tough to complete therapy.
Although the menopausal symptoms from aromatase inhibitors can be hard to deal with, there are things you can do that may ease these and other side effects. Talk with your health care provider about ways to treat them.
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 do not .
If you have trouble remembering to take your hormone therapy, a pillbox or setting an alarm on your watch or phone (you may be able to download an app) may help . However, you do not need to panic if you miss a day or two.
Learn more about the importance of following your breast cancer treatment plan.
Anastrozole, exemestane and letrozole are all available in generic forms. Generics cost less than name brand drugs, but are just as effective.
Medicare and many insurance providers offer prescription drug plans. One may already be included in your policy or you may be able to buy an extra plan for prescriptions.
You may also qualify for programs that help with drug costs or offer low-cost or free prescriptions.
Learn more about insurance plans and prescription drug assistance programs.
Susan G. Komen’s position on fairness in breast cancer medication coverage
Medications taken by mouth (oral) are usually covered under a health insurance plan’s prescription drug benefit rather than the plan’s medical benefit. As a result, people often find themselves facing high out-of-pocket costs when filling their prescriptions (sometimes costing thousands of dollars per month). High prescription drug costs are a barrier to care. High costs can prevent people from getting the medications prescribed by their health care provider.
Komen supports efforts at the state and federal levels that require insurers to provide coverage for oral breast cancer medications at a rate no less favorable than what they provide for IV medications to ensure patients have access to affordable, appropriate treatment for their cancer.
Komen Support Resources
Hormone Therapy Video
Facts for Life: Hormone Therapy
Breast Cancer 101 - Aromatase Inhibitors
1-877 GO KOMEN(1-877-465-6636)
What gives you strength during treatment?