ERBB2 and breast cancer: Gene expression profiling has led to classification of breast cancers into five groups: luminal A, luminal B, basal-like, HER2+ and normal breast-like (Perou et al, 2000; Sorlie et al, 2001, 2003; van de Rijn et al, 2002; Sotiriou et al, 2003; Nielsen et al, 2004) and importantly these groups have prognostic and predictive implications.