Title: Formestane
CAS Registry Number: 566-48-3
CAS Name: 4-Hydroxyandrost-4-ene-3,17-dione
Additional Names: 4-OHA
Manufacturers' Codes: CGP-32349
Trademarks: Lentaron (Novartis)
Molecular Formula: C19H26O3
Molecular Weight: 302.41
Percent Composition: C 75.46%, H 8.67%, O 15.87%
Literature References: Selective aromatase inhibitor. Prepn: R. D. Burnett, D. N. Kirk, J. Chem. Soc. Perkin Trans. 1 1973, 1830; J. Mann, B. Pietrzak, ibid. 1983, 2681; P. G. Ciattini et al., Synth. Commun. 22, 1949 (1992). Aromatase inhibition and effect on estrogen-dependent processes in vivo: A. M. H. Brodie et al., Endocrinology 100, 1684 (1977). Radioimmunoassay in plasma: J. Khubieh et al., J. Steroid Biochem. 35, 377 (1990). GC determn in plasma and urine: P. H. Degen, W. Schneider, J. Chromatogr. 565, 67 (1991). Pharmacokinetics and endocrine effects in breast cancer patients: M. Dowsett et al., Eur. J. Cancer 28, 415 (1992). Clinical evaluation in breast cancer: R. C. Coombes, J. Steroid Biochem. Mol. Biol. 43, 145 (1992).
Properties: Needles from aq methanol, mp 199-202° (Burnett, Kirk); also reported as crystals from ethyl acetate, mp 203.5-206° (Brodie). uv max (99.5% ethanol): 278 nm (e 11030). [a]D20 +181° (c = 7.7 in chloroform).
Melting point: mp 199-202° (Burnett, Kirk); mp 203.5-206° (Brodie)
Optical Rotation: [a]D20 +181° (c = 7.7 in chloroform)
Absorption maximum: uv max (99.5% ethanol): 278 nm (e 11030)
Therap-Cat: Antineoplastic (hormonal).
Keywords: Antineoplastic (Hormonal); Aromatase Inhibitors; Aromatase Inhibitors.
Formic Acid Formicin Formocortal Formoterol Formothion

Systematic (IUPAC) name
Clinical data
AHFS/ International Drug Names
Legal status  ?
CAS number 566-48-3 YesY
ATC code L02BG02
PubChem CID 11273
ChemSpider 10799 YesY
KEGG D07260 YesY
Synonyms 4-hydroxyandrost-4-ene-3,17-dione
Chemical data
Formula C19H26O3 
Mol. mass 302.408 g/mol
 N (what is this?)  (verify)

Formestane (Lentaron) is a type I, steroidal aromatase inhibitor. It is used in the treatment of estrogen-receptor positive breast cancer in post-menopausal women. It is available as an intramuscular depot injection.

Formestane is often used to suppress estrogen production 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 mild aromatase inhibitor.

Formestane has poor oral bioavailability and as such is no longer popular as many orally active aromatase inhibitors have been identified.

It is selective.[1]