A randomised comparison of oestrogen suppression with anastrozole and formestane in postmenopausal patients with advanced breast cancer.

The relative efficacy and tolerability of the aromatase inhibitors anastrozole (Arimidex) and formestane are assessed in a direct comparative trial in postmenopausal women with advanced breast cancer. Final results are available and reported here only for oestradiol suppression. Patients were randomised to receive either oral anastrozole, 1 mg once daily, or formestane, 250 mg every 2 weeks intramuscularly. In the anastrozole group, mean serum oestradiol levels fell from 32.1 pmol/l at baseline to 6.5 pmol/l at week 1, and similar levels of suppression were maintained over the next 3 weeks. In the formestane group, mean serum oestradiol levels fell from 31.0 pmol/l at baseline to 9.5 pmol/l at the week 1 assessment. In this group, serum oestradiol levels tended to rise by the 2- and 4-week measurements, i.e. immediately before the next injection was due. Based on the 2- and 4-week measurements, the mean falls in oestradiol levels were 79 and 58% in the anastrozole and formestane groups, respectively (p = 0.0001). More effective and consistent suppression of oestradiol was achieved with anastrozole at the therapeutic dose of 1 mg once daily, orally, than with formestane at the standard dose of 250 mg every 2 weeks, intramuscularly.