Tamoxifen Benefits and CYP2D6 Testing in Women With Hormone Receptor-Positive Breast Cancer

Cancer intervention strategies have been increasingly focused on developing therapies that are personalized and tailored to each individual's unique genetic profile. Evolving understanding of the metabolism and pharmacogenomics of tamoxifen, an early example of targeted therapy for women with hormone receptor-positive breast cancer, has created decision-making challenges for healthcare providers and their patients. This article reviews the pharmacology of tamoxifen, the genetics and physiology of the CYP2D6 enzyme system that has important effects on tamoxifen metabolism, and subset data analyses from large controlled, clinical trials that cast new light on previously held beliefs about the utility of CYP2D6 genotyping for predicting tamoxifen effectiveness and improved breast cancer outcomes in women with early-stage, hormone receptor-positive breast cancer.