Figure 1 The distribution of oestrogen receptor (ER) and Ki67 antigen in benign breast lesions visualised by indirect immunofluorescence using fluorochromes Cy3 (orange/red) for ER and fluorescein (green) for Ki67 antigen. (A) An apocrine cyst containing occasional Ki67+ cells but no ER + cells. (B) Duct ectasia showing mutual exclusion between ER and Ki67. (C) A solitary papilloma showing extensive ER positivity and containing occasional dual labelled cells. (D) Gynaecomastia showing pronounced ER positivity and containing occasional dual labelled cells.