THE APPLICATION OF BIOANALYTICAL METHOD OF TAMOXIFEN AND ITS ACTIVE METABOLITES FOR THERAPEUTIC DRUG MONITORING IN BREAST CANCER PATIENTS: A REVIEW

Breast cancer is the most common cancer around the world and in Indonesia. The most widely used agent for breast cancer treatment is tamoxifen, with a fixed dose of 20 mg per day. Tamoxifen is metabolized by cytochrome P450 3A4 (CYP3A4) and 2D6 (CYP2D6) to endoxifen and 4-hydroxytamoxifen, which have 30-to 100-fold more potent antiestrogenic activity than tamoxifen. High variations of CYP3A4 and CYP2D6 genes can lead to interpatient variability in its metabolites concentration. The dose can be increased to 40 or 60 mg per day based on individual needs. Therapeutic drug monitoring (TDM) is required to measure the concentration of tamoxifen and its metabolites to decide the individualized dose. The measurement of drug levels should use a sensitive, selective, accurate, precise, and reliable bioanalytical method. Various bioanalytical methods have been developed in several matrice s: urine, scalp hair, serum, plasma, dried blood spot (DBS), and volumetric absorptive microsampling (VAMS) samples, with different sample preparations, and frequently using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The bioanalytical method of tamoxifen and its metabolites in the DBS sample was more suitable in the TDM application due to the low invasive sampling technique, mor e stable sample, and rapid sample preparation. Therefore, it is more time-and cost-efficient than the other methods.