The negative association between the oestrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER-2) in breast cancer travels in both directions. ER+ tumours are less likely HER-2+ and HER-2+ tumours are less likely ER+.
Department of Obstetrics and Gynaecology, Multidisciplinary Breast Centre, University Hospitals Leuven, Herestraat 49, B-3000 Leuven, Belgium. Patrick.neven@uz.kuleuven.ac.be