Aromatase Inhibitors for Lowering Breast Cancer Risk

Aromatase inhibitors (drugs that lower estrogen levels) may someday prove to be as good as or even better than tamoxifen or raloxifene in reducing breast cancer risk, but they haven’t been well studied for this use. More study is needed to see who would most benefit and how long treatment should be continued.

What are aromatase inhibitors?

Aromatase inhibitors lower estrogen levels by stopping an enzyme in fat tissue (called aromatase) from changing other hormones into estrogen. These drugs don’t stop the ovaries from making estrogen. They only lower estrogen levels in women whose ovaries aren’t making estrogen (such as women who have already gone through menopause). The drugs in this class include:

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

Aromatase inhibitors are pills taken once a day.

Can aromatase inhibitors lower the risk of breast cancer?

Aromatase inhibitors are used mainly to treat hormone receptor-positive breast cancer, but are being studied to see if they can lower breast cancer risk. Early findings are promising, but they are not yet approved for this use in the US.

What are the risks and side effects of aromatase inhibitors?

The most common side effects of aromatase inhibitors are symptoms of menopause, such as hot flashes, night sweats, and vaginal dryness. These drugs can also cause muscle and joint pain. This side effect can be serious enough to cause some women to stop taking the drugs.

Unlike tamoxifen and raloxifene, aromatase inhibitors tend to speed up bone thinning, which can lead to osteoporosis. It is easy for people with osteoporosis to have broken bones.

Aromatase inhibitors may raise cholesterol. Women with pre-existing coronary heart disease who take an aromatase inhibitor may be at risk of having a heart problem.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: June 1, 2016 Last Revised: August 18, 2016

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