The characteristic metabolite pattern resulting from tamoxifen daily dosing of 20 mg to CYP2D6 EMs was demonstrated to be well tolerated and highly beneficial over the past four decades (Early Breast Cancer Trialists' Collaborative Group (EBCTCG), 1992, 1998, 2005; Stearns et al., 2003, 2004). This evidence concerns the gene CYP2D6 and breast cancer.