The treatment of breast cancer has changed dramatically during the past 15 years, with all patients now receiving long-term antihormonal therapies, whether it is tamoxifen (EBCTCG, 1998), aromatase inhibitors (ATAC Trialists' Group, 2002), or LHRH superagonists plus tamoxifen (Emens and Davidson, 2003). Here, CYP19A1 is linked to breast carcinoma.