Tamoxifen is an effective drug reducing the risk of dying from breast cancer. This study aims to validate and study the feasibility of serial assessments, including therapeutic drug monitoring of tamoxifen (TAM), 4-hydroxytamoxifen (4HT) and Z-endoxifen (Z-END) by capillary blood sampling.
A prospective, single-centre study including women with stage 0-3 breast cancer receiving adjuvant tamoxifen 20 mg/day for a minimum of 2 months. Study design: Blood samples for repeated measurement of TAM, 4HT and Z-END were drawn capillary in total at 4-time points, at inclusion (baseline), and after 1, 2, and 3 weeks for each participant; and venously in total at two time-points, at inclusion (baseline), and after 3 weeks for each participant. At baseline, the capillary blood test concentrations of TAM, 4HT and Z-END were taken first by the research nurse and second by the patient. At each time, participants will be asked to leave 1 vial of capillary blood using the rhelise™ kit and 2 samples of conventional venous blood for blood and plasma. Primary Objective To validate the rhelise™ kit for monitoring TAM, 4HT and Z-END among patients who have ongoing adjuvant tamoxifen by testing for equivalence between concentrations found in the capillary sample and the venous blood sample (gold standard). Primary endpoint Blood concentrations and correlations of TAM, 4HT and Z-END at baseline and 3 weeks by capillary and venous blood sampling (whole blood/plasma). Secondary objectives To validate user acceptability and feasibility of self-testing the capillary kit by comparing the capillary blood test concentrations of TAM, 4HT and Z-END taken by the patient to the capillary sample taken by the research nurse. Secondary endpoints Capillary blood test concentrations of TAM, 4HT and Z-END were taken by the patient and the research nurse at baseline.
A capillary sampling kit was used for 40 participants. Mean TAM, 4HT and Z-END concentrations did not differ significantly in the 3 types of samples. Mean capillary TAM, 4HT and Z-END concentrations did not differ significantly between nurse and patient.
TDM of TAM using capillary blood sampling is feasible.
Elham Hedayati, Karolinska University Hospital.
Vinnova & Karolinska University Hospital, Karolinska Institutet.
S. Rehnmark, H. Randahl: Financial Interests, Personal and Institutional, Ownership Interest: Redhotdiagnostics AB. A. Lindqvist: Financial Interests, Personal and Institutional, Full or part-time Employment: Redhotdiagnostics AB. All other authors have declared no conflicts of interest.