CYP19A1 and ductal breast carcinoma in situ: However, we have clearly demonstrated a significant fall in the proliferation in DCIS epithelium following a period of oestrogen withdrawal in OR-positive (but not in OR-negative) tumours, consistent with that reported in OR-positive IBC after treatment with either aromatase inhibitors (Ellis et al, 2001; Miller et al, 2001) or tamoxifen (Chang et al, 2000).