CYP19A1 and ductal breast carcinoma in situ: Its use has become more common in the United States, with approximately 60% of all DCIS cases having BCS receiving it in recent years.16 Adjuvant ET for hormone receptor-positive DCIS tumours, with tamoxifen or aromatase inhibitors (e.g. Anastrozole), may improve local control in hormone-responsive disease12,17–20 and reduce the risk of BC recurrence, but survival benefit is unproven.4,12 Data on outcome by oestrogen receptor (ER) status of the DCIS are absent in most randomised trials.