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Clinical data
Trade names Lentaron, others
Synonyms 4-Hydroxyandrost-4-ene-3,17-dione
AHFS/ International Drug Names
Routes of
Intramuscular injection
Drug class Aromatase inhibitor; Antiestrogen
ATC code
CAS Number
PubChem CID
ECHA InfoCard 100.153.838 Edit this at Wikidata
Chemical and physical data
Formula C19H26O3
Molar mass 302.408 g/mol
3D model (JSmol)
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Formestane, formerly sold under the brand name Lentaron among others, is a steroidal, selective aromatase inhibitor which is used in the treatment of estrogen receptor-positive breast cancer in postmenopausal women.[1] The drug is not active orally, and was available only as an intramuscular depot injection. Formestane was not approved by the United States FDA and the injectable form that was used in Europe in the past has been withdrawn from the market.[2] Formestane is an analogue of androstenedione.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.
  2. ^ []