Aromatase inhibitor

Aromatase inhibitors (AIs) are a class of drugs that block the enzyme aromatase, which is responsible for converting androgens into estrogens.^[1] They are primarily used in the treatment of hormone receptor-positive breast cancer, particularly in postmenopausal women,^[2] but can also be used in premenopausal women when combined with ovarian suppression therapy.^[3] AIs are also used in men for conditions such as gynecomastia and hormone-sensitive cancers,^[4] and may be used off-label to manage estrogen levels during testosterone therapy.^[5] Additionally, they are sometimes used for chemoprevention in individuals at high risk of developing breast cancer.^[6]

Aromatase is the enzyme that catalyzes a key aromatization step in the synthesis of estrogen. It converts the enone ring of androgen precursors such as testosterone, to a phenol, completing the synthesis of estrogen. As such, AIs are estrogen synthesis inhibitors. Because hormone-positive breast and ovarian cancers are dependent on estrogen for growth, AIs are taken to either block the production of estrogen or block the action of estrogen on receptors.