Growth-regulatory proteins switch functions via reversible phosphorylation events. The most commonly overexpressed phosphoprotein in human cancers is ErbB2 (HER2/neu), an orphan receptor that is activated by ligand-dependent hetero-oligomerisation with homologous receptor tyrosine kinases such as the heregulin receptor ErbB3 or the epidermal growth factor receptor (EGFR).1,2 Expression of this phenotype in breast cancer is an adverse prognostic factor that predicts reduced benefit from hormonal and standard-dose cytotoxic therapies.