Mayo Clinic researchers have recommended CYP2D6 gene testing for postmenopausal women about to begin tamoxifen therapy. This data confirms that women with an inherited deficiency in the CYP2D6 gene, which is important for the metabolism of tamoxifen, have a nearly fourfold higher risk of early breast cancer recurrence compared to women who have not inherited the deficiency. The research findings, announced jointly by investigators from Mayo Clinic and the Austrian Breast and Colorectal Cancer Study Group (ABCSG) confirmed results from a previous study conducted by Mayo Clinic.