Aromatase inhibitors are primarily used to treat hormone receptor–positive breast cancer in postmenopausal people by preventing the conversion of androgen hormones to estrogen.
They may also be used for other conditions, such as McCune-Albright syndrome, infertility, and endometriosis.
Early and Advanced Breast Cancer
In postmenopausal women, the primary source of estrogen isn’t the ovaries. Instead, the enzyme aromatase works inside tissues, such as skin, muscles, and fat, to convert androgens into estrogen. AIs block this enzyme, preventing the conversion of androgens into estrogen. Since ER-positive breast cancer thrives on estrogen, AIs slow the cancer’s growth.
Breast Cancer Following Tamoxifen Therapy
Tamoxifen is a type of hormone therapy that blocks the effects of estrogen on cancer cells, and is usually the first choice for HR-positive breast cancer in women who have not yet gone through menopause.
Sometimes, however, the cancer no longer responds to tamoxifen. In this case, switching to an aromatase inhibitor can be an effective solution for slowing cancer progression. If the individual is still premenopausal at the time of the switch, other treatments will be needed to suppress the ovaries (and induce menopause).
Breast Cancer Prevention in People at Higher Risk
Aromatase inhibitors may be given to postmenopausal women with a higher than average risk of breast cancer to lower their risk.
Two aromatase inhibitors — anastrozole and exemestane — have been shown in large clinical studies to lower breast cancer risk in postmenopausal women, but they are not yet approved by the U.S. Food and Drug Administration (FDA) for this use.
McCune-Albright Syndrome
McCune-Albright syndrome is a rare genetic disorder that affects the bones, skin, and endocrine (hormone) system. It causes scarred bone tissue (called fibrous dysplasia), light brown spots on the skin (called café au lait skin pigmentation), and an overproduction of growth-regulating hormones.
In girls, this syndrome commonly causes puberty to start too early. Aromatase inhibitors may be given to reduce the symptoms of precocious puberty and to stop puberty from progressing.
Infertility
Letrozole (Femara) is a type of aromatase inhibitor that may be used to induce ovulation in women with polycystic ovarian syndrome (PCOS) who have infrequent or absent periods. Results from a 2022 study in women with PCOS and infertility demonstrated that treatment with letrozole improved pregnancy and live birth rates.
Endometriosis
Endometriosis is a gynecological condition in which tissue similar to the lining of the uterus grows outside the uterus, causing pelvic pain and infertility.
Aromatase inhibitors may be a potential option for women with endometriosis who have not found relief from standard treatments, but more research is needed to learn about its effectiveness.
