Published: February 2010
Prescriber Update 31(4): 1
Prescribers are advised that case reports of breast cancer have been reported in male patients following the use of finasteride.
Finasteride is a specific inhibitor of type II 5α-reductase, an intracellular enzyme that metabolises testosterone into the more potent androgen dihydrotestosterone (DHT).1
Finasteride is approved in New Zealand for the treatment of benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern hair loss). The recommended dose for treatment of BPH is 5mg daily; the recommended dose for male pattern hair loss is 1mg daily.1,2
The United Kingdom Medicines and Healthcare products Regulatory Agency (MHRA) has recently published a report on the possible association between the use of finasteride and breast cancer in males. The MHRA has concluded that an association can not be excluded.3
Up to November 2009, fifty cases of male breast cancer have been reported worldwide with 5 mg finasteride and three cases with the 1 mg dose. However, clinical trials found that the incidence of male breast cancer for the 5 mg dose of finasteride was not significantly increased when compared to those not exposed to finasteride.3
A possible mechanism for this association relates to the pharmacodynamics of finasteride. Finasteride use leads to decreases in DHT levels that are accompanied by increases in testosterone and oestradiol levels. The increase in sex steroids has the potential to increase the risk of breast cancer.
Prescribers are reminded to advise patients to report any changes in breast tissue such as lumps, pain or nipple discharge, to their doctor.
Medsafe is currently working with the New Zealand sponsors of finasteride containing products to update the data sheets, which are available at: