Clinical and endocrine effects of the oral aromatase inhibitor vorozole in postmenopausal patients with advanced breast cancer.

Vorozole is an orally active, nonsteroidal aromatase inhibitor. Twenty-four postmenopausal patients with advanced breast cancer who had relapsed after treatment with tamoxifen received three separate daily doses of vorozole (1, 2.5, and 5 mg) each for 1 month in a randomized, double-blind, phase II study. There was significant suppression (P < 0.001) of serum estradiol at all three doses (median reduction, 91, 90, and 89%, respectively). There was a significant trend (P = 0.02) for estradiol to be suppressed below the detection limit of the assay (3 pmol/liter) more frequently with an increasing dose of vorozole; 13, 31, and 40% respectively. Estrone and estrone-sulfate levels were likewise reduced at each dose by 52-55% and 64-69%, respectively. There was no significant effect at any dose on aldosterone, testosterone, androstenedione, 17 alpha-hydroxyprogesterone, or thyroid-stimulating hormone levels. A small reduction in cortisol was seen at the 5 mg dose, although the relevance is unclear given that 17 alpha-hydroxyprogesterone levels did not rise. Eight patients (33%) achieved an objective response (2 complete remission, 6 partial remission) with a median response duration of 13 months. Four patients (17%) achieved disease stabilization for more than 6 months. Patients who had responded previously to tamoxifen were more likely to respond to vorozole. There were no significant clinical side effects and the drug was well tolerated. These data suggest that vorozole is a potent and selective oral aromatase inhibitor for use in postmenopausal breast cancer.