What is "formestane"

n. An aromatase inhibitor drug that is used to treat estrogen-receptor positive breast cancer.

Formestane (trade name Lentaron) is a type I, steroidal, selective aromatase inhibitor. It is used in the treatment of estrogen receptor-positive breast cancer in postmenopausal women. The drug is not active orally, and is instead available only as an intramuscular depot injection. Because of this, it is no longer popular as many orally active aromatase inhibitors have been identified and introduced. Formestane is an analogue of androstenedione.

Formestane is often used to suppress the production of estrogens from anabolic steroids or prohormones. It also acts as a prohormone to 4-hydroxytestosterone, an active steroid which displays weak androgenic activity in addition to acting as a weak aromatase inhibitor.