Second generation aromatase inhibitor--4-hydroxyandrostenedione

4-hydroxyandrostenedione is a steroidal, suicide substrate inhibitor of aromatase, which has been widely tested in postmenopausal breast cancer patients. It is highly specific with the only notable endocrine changes other than oestrogen suppression being a dose-related suppression of sex-hormone binding globulin when the drug is given orally (a reflection of the drug's minor androgenic activity). Intramuscular administration of 250 mg every second week is the schedule of choice. This achieves peripheral aromatase inhibition of about 85% and oestradiol suppression of about 65%. The drug is usually used second-line, after tamoxifen, with an overall response rate in unselected patients of 26%. Side-effects are minimal and consist almost entirely of local reactions at the site of injection. 4-hydroxyandrostenedione is therefore a useful new treatment option as the first selective aromatase inhibitor to have wide clinical availability.