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Clinical data
Trade names Lentaron
AHFS/ International Drug Names
ATC code
Synonyms 4-Hydroxyandrost-4-ene-3,17-dione
CAS Number
PubChem CID
ECHA InfoCard 100.153.838
Chemical and physical data
Formula C19H26O3
Molar mass 302.408 g/mol
3D model (Jmol)
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Formestane (trade name Lentaron), also known as 4-hydroxyandrost-4-ene-3,17-dione, is a type I, steroidal, selective aromatase inhibitor.[1] 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.


  1. ^ Pérez Carrión R, Alberola Candel V, Calabresi F, et al. (1994). "Comparison of the selective aromatase inhibitor formestane with tamoxifen as first-line hormonal therapy in postmenopausal women with advanced breast cancer". Ann. Oncol. 5 Suppl 7: S19–24. PMID 7873457.