Tamoxifen metabolites in patients on long-term adjuvant therapy for breast cancer.


Serum concentrations of tamoxifen, 4-OH-tamoxifen, N-desmethyltamoxifen, and metabolites E and Y were assayed to assess the variation of tamoxifen-metabolism during short-term and long-term endocrine treatment for breast cancer. Once steady-state was achieved, serum levels of tamoxifen and its metabolites in individual patients were stable in the short (10 weeks) and long term (over 7 years) (coefficient of variation [CV], 10-15%), but the variation between individuals (CV 50-70%) was high. Serum tamoxifen and N-desmethyltamoxifen levels were not correlated with indices of obesity. Thus this does not explain the large variation between individuals. In addition to the metabolites that were measured, 4-hydroxy-N-desmethyltamoxifen was tentatively identified in patients' serum. Overall, this study demonstrated that the metabolites of tamoxifen are stable (i.e. no metabolic tolerance) for up to 10 years of drug administration.

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@article{LanganFahey1990TamoxifenMI, title={Tamoxifen metabolites in patients on long-term adjuvant therapy for breast cancer.}, author={Susan M. Langan-Fahey and Douglass C. Tormey and V . Craig Jordan}, journal={European journal of cancer}, year={1990}, volume={26 8}, pages={883-8} }