Aromatase Inhibitors

Overview

What is an aromatase inhibitor?

An aromatase inhibitor (AI) is a type of hormone therapy for cancer. Healthcare providers use aromatase inhibitors to treat hormone receptor-positive (ER-positive) breast cancer. ER-positive breast cancer often affects women and people assigned female at birth (AFAB) who are age 50 and older.

Aromatase inhibitors work by reducing the amount of estrogen in your body. Estrogen is an essential hormone. It supports your sexual and reproductive health. It also regulates important processes in your skeletal, cardiovascular and central nervous systems that affect your overall health.

But high estrogen levels may increase your risk of developing ER-positive breast cancer. Aromatase inhibitors block the enzyme aromatase, which turns other hormones into estrogen. By reducing your estrogen levels, aromatase inhibitors keep cancerous cells from growing and spreading.

Providers typically use aromatase inhibitor therapy for people with breast cancer who’ve gone through menopause. (Women and people AFAB who haven’t gone through menopause typically don’t receive aromatase inhibitor therapy because their ovaries are still making estrogen.)

Aromatase inhibitors also keep ER-positive breast cancer from recurring, or coming back, after breast cancer surgery. If you have an increased risk of developing ER-positive breast cancer, taking an aromatase inhibitor may reduce your risk.

How common is this treatment?

It’s very common. ER-positive cancer affects about 8 in 10 people. Providers use aromatase inhibitor therapy as front-line or initial treatment for ER-positive breast cancer. They may also prescribe aromatase inhibitor therapy if:

• You’ve had surgery for ER-positive breast cancer, to reduce the risk the cancer will come back.
• You have ER-positive breast cancer that’s spread to nearby lymph nodes.
• You have metastatic (spread outside your breast) ER-positive breast cancer that’s spread to your organs. Breast cancer may spread to your lungs, bones, brain or liver.
• You develop ER-positive breast cancer before you’ve gone through menopause. You may have an additional treatment to block ovarian estrogens.
• You’re at increased risk of developing ER-positive breast cancer. Studies show certain aromatase inhibitors reduce breast cancer risk. The U.S. Food and Drug Administration (FDA) hasn’t approved this use.
• You’re a man or assigned male at birth (AMAB) with ER-positive breast cancer. (While estrogen is typically considered a female hormone, men and people AMAB have estrogen, just at lower levels than people who are AFAB.) In this case, your provider may combine aromatase inhibitor therapy with estrogen-blocking therapy.