Aromatase inhibitor

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

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.