Tamoxifen is an antiestrogen drug with concentration dependent properties, with z-endoxifen known as active metabolite. Until know therapeutic range for z-endoxifen to improve treatment response was not known. Variation response on tamoxifen can be cause of genetic polymorphism CYP2D6 that can be different between interindividul and ethnic.~The aim of this study is to determine phenotype and genotype of CYP2D6 as predictors of z-endoxifen concentrations in plasma of outgoing patients treated with tamoxifen for at least 4 months
This study is an observational study to determine phenotype and genotype of CYP2D6 as predictors of z-endoxifen concentrations in plasma of outgoing patients treated with tamoxifen for at least 4 months