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Concentration of tamoxifen and its major metabolites in hormone responsive and resistant breast tumours

MacCallum, J.; Cummings, J.; Dixon, J. M.; Miller, W. R.


J. Cummings

J. M. Dixon

W. R. Miller


Patients treated with tamoxifen (TAM) for primary breast cancer often manifest de novo or acquired resistance, possibly through changes in drug metabolism. Using solid-phase extraction methods and reversed-phase high-performance liquid chromatography separations, levels of TAM and metabolites 4-hydroxytamoxifen (4OH) and desmethyltamoxifen (DMT) have been measured in plasma and tumour tissue from breast cancer patients treated with TAM for at least 3 months. Patients were categorized into those with tumours responding to TAM and those showing de novo or acquired resistance. Levels of TAM, 4OH and DMT in both plasma and tissue samples were correlated with clinical response, length of treatment and patient weight. Interesting results included accumulation of 4OH in tumour tissues over time in all patients, with significance reached in the acquired resistance group. In addition, significantly lower levels of 4OH and DMT were found in plasma taken from responding patients after 3 months of treatment when compared to non-responding patients, and a small group of ER-poor patients showed significantly lower levels of all three species in plasma when compared to other patients. Whilst not explaining TAM resistance in all cases, these differences could account for the development of resistance to TAM treatment in certain subgroups of patients.

Journal Article Type Article
Online Publication Date Apr 27, 2000
Publication Date 2000-05
Deposit Date May 30, 2022
Journal British Journal Cancer
Print ISSN 0028-0836
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 82
Issue 10
Pages 1629-1635
Public URL