INFLUENCE OF ANASTROZOLE (ARIMIDEX), A SELECTIVE, NONSTEROIDAL AROMATASE INHIBITOR, ON IN-VIVO AROMATIZATION AND PLASMA ESTROGEN-LEVELS IN POSTMENOPAUSAL WOMEN WITH BREAST-CANCER

The effect of anastrozole ('Arimidex'. ZD1033), a new, selective non-s teroidal aromatase inhibitor on in vivo aromatisation and plasma oestr ogen levels was evaluated in post-menopausal women with breast cancer. Twelve patients progressing after treatment with tamoxifen were rando mised to receive anastrozole 1 mg or 10 mg once daily for a 28 day per iod in a double-blinded crossover design. In vivo aromatisation and pl asma oestrogen levels were determined before commencing treatment and at the end of each ii-week period. Treatment with anastrozole 1 and 10 mg reduced the percentage aromatisation from 2.25% to 0.074% and 0.04 3% (mean suppression of 96.7% and 98.1% from baseline) and suppressed plasma levels of oestrone, oestradiol and oestrone sulphate by greater than or equal to 86.5%, greater than or equal to 83.5% and greater th an or equal to 93.5% respectively, irrespective of dose. Notably. seve ral patients had their oestrone and oestradiol values suppressed benea th the sensitivity limit of the assays. In conclusion. anastrozole was found to be highly effective in inhibiting in vivo aromatisation with no difference in efficacy between the two drug doses. Contrary to pre vious studies on other aromatase inhibitors, this study revealed an in ternal consistency between the percentage aromatase inhibition and sup pression of plasma oestrone sulphate.