CYP2D6 phenotype, tamoxifen metabolites and biomarkers modulation. (a) Tamoxifen and its major metabolite plasma level based on CYP2D6 phenotypes. A significant accumulation of N-desmethyltamoxifen is noticed in the reduced activity phenotype. (b) Ki-67 labeling index (LI) and sex hormone-binding globulin (SHBG) modulation based on the different phenotypes. A significant decrease of Ki-67 LI and an increase of SHBG can be seen in the active group.