Clinical Oncology/Epidemiology

Influence of anastrozole (Arimidex), a selective, non-steroidal aromatase inhibitor, on in vivo aromatisation and plasma oestrogen levels in postmenopausal women with breast cancer

Abstract

The effect of anastrozole ('Arimidex', ZD1033), a new, selective, non-steroidal aromatase inhibitor on in vivo aromatisation and plasma oestrogen levels was evaluated in post-menopausal women with breast cancer. Twelve patients progressing after treatment with tamoxifen were randomised to receive anastrozole 1 mg or 10 mg once daily for a 28 day period in a double-blinded crossover design. In vivo aromatisation and plasma oestrogen levels were determined before commencing treatment and at the end of each 4-week period. Treatment with anastrozole 1 and 10 mg reduced the percentage aromatisation from 2.25% to 0.074% and 0.043% (mean suppression of 96.7% and 98.1% from baseline) and suppressed plasma levels of oestrone, oestradiol and oestrone sulphate by > or = 86.5%, > or = 83.5% and > or = 93.5% respectively, irrespective of dose. Notably, several patients had their oestrone and oestradiol values suppressed beneath 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 previous studies on other aromatase inhibitors, this study revealed an internal consistency between the percentage aromatase inhibition and suppression of plasma oestrone sulphate.

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Part of the work was presented at the Fourth Nottingham International Breast Cancer Conference, September 1995, at the ECCO 8 Conference in Paris, October 1995, and at the 18th Annual San Antonio Breast Cancer Symposium in December 1995

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Geisler, J., King, N., Dowsett, M. et al. Influence of anastrozole (Arimidex), a selective, non-steroidal aromatase inhibitor, on in vivo aromatisation and plasma oestrogen levels in postmenopausal women with breast cancer. Br J Cancer 74, 1286–1291 (1996). https://doi.org/10.1038/bjc.1996.531

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