Prevention of spontaneous tumours in female rats by fadrozole hydrochloride, an aromatase inhibitor.

Mammary tumours are oestrogen dependent in female Sprague-Dawley rats and in a significant proportion of women, so pharmacological treatment to inhibit oestrogen production is a valuable therapeutic measure to prevent or slow the progression of disease. Here we show that a non-steroidal aromatase inhibitor, which competitively inhibits the conversion of androstenedione to oestrone, prevents the development of both benign and malignant spontaneous mammary neoplasms in female Sprague-Dawley ats. It also slows the spontaneous development of pituitary pars distalis adenomas in female rats, and reduces the incidence of spontaneous hepatocellular tumours in male and female rats.