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Dear Editor,
I read with great interest the article by de Souwer et al. [1] in which they study the pharmacokinetics and -dynamics of tamoxifen in older women with non-metastatic breast cancer. According to their findings, older women receiving steady-state adjuvant tamoxifen treatment have higher serum concentrations of tamoxifen and its demethylated metabolites, such as endoxifen, than younger women. The authors put forth a number of theories to explain why older patients had higher endoxifen concentrations. There was a missing explanation. Endoxifen levels in older patients may also be higher as creatinine clearance gradually decreases with age and urinary elimination is a major route of endoxifen excretion [2]. This subject deserves more explanation.
References
Souwer ETD, Sanchez-Spitman A et al (2023 Apr) Tamoxifen pharmacokinetics and pharmacodynamics in older patients with non-metastatic breast cancer. Breast Cancer Res Treat 17. https://doi.org/10.1007/s10549-023-06925-zEpub ahead of print
Kisanga ER, Mellgren G, Lien EA (2005) Excretion of hydroxylated metabolites of tamoxifen in human bile and urine. Anticancer Res 25:4487–4492
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Altundag, K. Is there any association between declined creatinine clearence and higher endoxifen levels in older patients with non-metastatic breast cancer?. Breast Cancer Res Treat 201, 147 (2023). https://doi.org/10.1007/s10549-023-07004-z
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DOI: https://doi.org/10.1007/s10549-023-07004-z