Clinical evaluation of dried blood spots obtained from a fingerprick for the determination of tamoxifen and endoxifen levels

DBS samples to determine the pharmacokinetics of tamoxifen in a ‘real life’ cohort will be collected during a routine visit to the Antoni van Leeuwenhoek hospital where a serum sample is obtained as part of clinical care.

No relationship between DBS and serum concentrations has been established yet for tamoxifen and endoxifen. This would enable sample collection by means of a simple fingerprick. The DBS to serum ratio of tamoxifen and endoxifen has to be defined in simultaneously drawn DBS and serum samples of patients using tamoxifen.

Tamoxifen and endoxifen serum concentrations are linearly related to DBS concentration

1 timepoint; a paired sample will be obtained a serum sample and a dried blood spot sample

Patients are treated with tamoxifen on a dose according to the prescription of the physician. No further intervention is needed. A DBS sample will be obtained simultaneously with the serum sample that is obtained for regular clinical care.