There has been a continuing decline in breast cancer mortality over the last 10 years, which is partly due to the continued development of new therapy options for breast cancer, including the third-generation aromatase inhibitors (letrozole, anastrozole, and exemestane) as the hormonal therapies of choice for postmenopausal patients (Coombes et al, 2004; ATAC Trialists' Group, 2005; Goss et al, 2005; The Breast International Group (BIG) 1-98 Collaborative Group, 2005). Here, CYP19A1 is linked to breast cancer.