Aromatase Inhibitors
An aromatase inhibitor is a type of hormonal therapy medicine that may be recommended for you if you’ve been diagnosed with hormone receptor-positive breast cancer.
There are three aromatase inhibitors doctors use to treat breast cancer:
Arimidex (chemical name: anastrozole)
Aromasin (chemical name: exemestane)
Femara (chemical name: letrozole)
How do aromatase inhibitors work?
Aromatase inhibitors work by blocking the enzyme aromatase, which turns the hormone androgen into small amounts of estrogen in the body. Hormone receptor-positive breast cancer relies on estrogen to grow. Aromatase inhibitors don’t work on hormone receptor-negative breast cancer.
Who gets aromatase inhibitors?
Aromatase inhibitors can’t stop the ovaries from making estrogen. As a result, doctors prescribe these medicines mainly to those who are post-menopausal because their ovaries don’t produce estrogen anymore. Before menopause, most of the estrogen in the body is made by the ovaries.
Research suggests that an aromatase inhibitor can be combined with medicine that stops the ovaries from working (ovarian suppression medicine) to treat hormone receptor-positive breast cancer with a high risk of recurrence in those who are pre-menopausal.
How long do you take an aromatase inhibitor?
All the aromatase inhibitors are pills taken once a day. How long you take an aromatase inhibitor depends on the stage of the cancer and the medicine recommended for you.
If you’ve been diagnosed with early-stage, hormone receptor-positive breast cancer, you usually take an aromatase inhibitor for at least five years after surgery to reduce the risk of recurrence. In some cases, another five years of the aromatase inhibitor may be recommended, for a total of 10 years of hormonal therapy.
If you’ve already taken tamoxifen for two to three years because you were pre-menopausal when first diagnosed, your doctor may recommend that you then take an aromatase inhibitor for either two or three years — for a total of five years of hormonal therapy. Your doctor may recommend that you continue the aromatase inhibitor for another five years after the first five years have been completed.
If you’ve been diagnosed with advanced-stage, hormone receptor-positive breast cancer you take any of the aromatase inhibitors for as long as you’re getting benefits from the medicine.
Side effects of aromatase inhibitors
Like all hormonal therapy medicines, aromatase inhibitors can cause side effects. Bone and joint pain and stiffness are the most common.
If you’re having problematic side effects from taking an aromatase inhibitor, tell your doctor right away. You may be able to take a different hormonal therapy medicine.
Listen to the episode of The Breastcancer.org Podcast featuring Ashish Khanna, MD, explaining how and why aromatase inhibitors cause side effects and how those side effects can be eased.
You can talk with others taking an aromatase inhibitor or other hormonal therapy medicine in the Breastcancer.org Community.
— Last updated on April 29, 2025 at 9:19 PM
