ErbB2 is a ligand-less member of the ErbB/epidermal growth factor (EGF) tyrosine kinase receptor family that enhances mitogenic signalling: by being constitutively active, by dimerising as a preferred partner with other ErbB members that in breast cancer can also be overexpressed, and by resisting endocytic degradation and returning to the cell surface [2-5]. This evidence concerns the gene EGFR and breast cancer.