NR4A1 and neoplasm: Although these observations may reflect sampling error within heterogeneous tumours, immunostaining on needle core biopsies in a previously reported series of 236 patients treated without intervening chemotherapy was highly representative of hormone receptor status in the entire resected tumour (Taucher et al, 2003a), suggesting that sampling error does not account for the observed hormone receptor ‘upregulation’ seen in some cases.