Determination of tamoxifen and biologically active metabolites in human breast tumours and plasma

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Abstract

This work describes the measurement of the antioestrogenic drug, tamoxifen, and two of its biologically active metabolites in the plasma and tumour tissue of patients with primary breast cancer. All three compounds were detected at high concentrations relative to those of oestradiol, with which tamoxifen competes for binding to specific receptors in tumour cells. N-desmethyltamoxifen was the more abundant metabolite in both plasma and tissue, where its concentration exceeded that of the parent drug. An hydroxylated metabolite, metabolite B, was present at about 2% the concentration of tamoxifen in both plasma and tumours. The high concentrations of these compounds measured in human tissue were therefore similar to those previously found to be capable of preventing the specific binding of oestradiol to its receptors in vitro.

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