CYP19A1 and neoplasm: Studies of patients with IBC have shown that early changes (<3 weeks) in cell proliferative indices and PR expression occur after antioestrogen therapy (Clarke et al, 1993; Chang et al, 2000; Dowsett et al, 2001a; Robertson et al, 2001; Harper-Wynne et al, 2002) in OR-positive (but not OR-negative) tumours and these changes are accepted as surrogate markers of clinical tumour response, with tamoxifen treatment increasing (Chang et al, 2000; Robertson et al, 2001) and aromatase inhibitor therapy decreasing PR expression (Miller et al, 2001).