The effects of T exposure on breast cancer development have been recently investigated in a prospective 10 year cohort study enrolling 1267 pre- and postmenopausal women receiving implants of T to treat the symptoms of androgen deficiency or T implants in combination with the aromatase inhibitor anastrozole (a therapeutic option for estrogen excess, obesity and breast cancer prevention). This evidence concerns the gene CYP19A1 and breast carcinoma.