Clinical evaluation of dried blood spots for the determination of tamoxifen and endoxifen levels

Tamoxifen, a selective estrogen receptor modulator, is widely used for the
treatment and prevention of breast cancer. The steady state concentration of
its most active metabolite, endoxifen, is a proposed predictor of tamoxifen
efficacy. It is suggested that there is a minimum serum concentration above
which endoxifen is effective against the recurrence of breast cancer. Current
practice is to analyze tamoxifen and metabolite concentrations in serum, blood
samples are collected when patients visit the Antoni van Leeuwenhoekhospital.

Clinical evaluation of dried blood spot (DBS) assay, by determining the ratio
between DBS and serum levels of tamoxifen and endoxifen and to investigate if
patients can obtain useful DBS at home.

Patients treated with tamoxifen who undergo venapuncture are asked if they are
willing to obtain a DBS sample at the same time. For the feasiblity part,
patients are asked if they are willing to self-obtain a DBS sample through a
fingerprick. They will be instructed at the Antoni van Leeuwenhoekhospital.

not applicable