356 A randomised, double-blind, multicentre crossover trial to evaluate in-vivo inhibition of aromatase by arimidex (ZD1033) (1 mg and 10 mg PO OD) in postmenopausal women with breast cancer

Abstract

ARIMIDEX (A) is a new aromatase inhibitor which has been shown to be a potent and highly selective in Phase I studies. It has also been evaluated in multicentre studies in the US and Europe for comparative clinical efficacy against megestrol acetate in postmenopausal women with advanced breast cancer. In this study we have compared the effect of once daily orally administered A (1 and 10 mg) on whole body aromatisation in 10 pts with breast cancer using a modification of the method described by Jacobs et al. (1991). A was well tolerated at both doses. Whole body aromatase was reduced by approx 95% after 28 days of treatment with either dose of A and the plasma concentration of oestrone, oestrone sulphate and oestradiol by >80; >90 and >80% respectively. Whereas the levels of AO showed no consistent change. These data indicate that 1 mg OD PO of A can maximally inhibit aromatisation in pts and that this is associated with a profound decrease in circulating estrogens.