CYP19A1 and breast carcinoma: Currently, letrozole is the only aromatase inhibitor licensed for use as neoadjuvant therapy, based on the results of the P024 trial (Ellis et al, 2001), where more women with oestrogen receptor-positive (ER+ve) primary breast cancer who received letrozole went on to receive breast conserving surgery (60% responded and 48% underwent successful breast-conserving surgery) compared with tamoxifen (41% responded and 36% underwent breast conservation).