CYP19A1 and breast cancer: The third-generation aromatase inhibitors (AIs), anastrozole, letrozole and exemestane, which prevent the conversion of androgens to estrogens by reversibly or irreversibly inhibiting the aromatase enzyme, have shown benefits over tamoxifen, in both adjuvant and metastatic treatment for postmenopausal hormone-responsive breast cancer women [1]–[5].