Because of their greater efficacy in reducing recurrences as well as their better tolerability profile, the third-generation aromatase inhibitors (ais), including anastrozole (Arimidex: AstraZeneca, Mississauga, ON), letrozole (Femara: Novartis Pharmaceuticals Canada, Dorval, QC), and exemestane (Aromasin: Pfizer Canada, Kirkland, QC), are increasingly being recommended as adjuvant therapy in postmenopausal women with breast cancer. This evidence concerns the gene CYP19A1 and breast cancer.