CYP19A1 and breast cancer: Aromatase inhibitor or fulvestrant is recommended as treatment choice for postmenopausal advanced breast cancer after tamoxifen treatment failure; steroidal aromatase inhibitor (with or without everolimus) or fulvestrant 500 mg is recommended as treatment choice for postmenopausal advanced breast cancer after non-steroidal aromatase inhibitor treatment failure by the most recent Chinese Breast Cancer Guidelines [17].