Identification of the aromatase inhibitor letrozole in urine by gas chromatography/mass spectrometry.

Letrozole (1-(bis-(4-cyanophenyl)methyl)-1,2,4-triazole) is used therapeutically as a non-steroidal aromatase inhibitor (Femara) to treat hormone-sensitive breast cancer in postmenopausal women. For doping purposes it may be used to counteract the adverse effects of an extensive abuse of anabolic androgenic steroids (gynaecomastia) and to increase the testosterone concentration by stimulation of the testosterone biosynthesis. The use of aromatase inhibitors has been prohibited by IOC/WADA regulations for male and female athletes since September 2001 and January 2005, respectively. Spot urine samples from women suffering from metastatic breast cancer and being treated with letrozole were collected and analysed to develop/optimise the detection system for metabolites of letrozole to allow the identification of athletes who do not comply with the internationally prohibited use of this cancer drug. The assay was based on gas chromatography/mass spectrometry (GC/MS) and the main metabolite of letrozole (bis-4-cyanophenylmethanol) was identified by comparison of its mass spectrum and retention time with that of a bis-4-cyanophenylmethanol reference. The full-scan spectrum, diagnostic ions and a validation of the method for the analysis of bis-4-cyanophenylmethanol are presented.