ERBB2 and invasive breast carcinoma: Based on gene expression profiling studies (Sorlie et al, 2001; Sorlie et al, 2003), invasive breast cancer can be divided into several subtypes: the basal-like, characterised by the expression of the CK5/6 and or EGFR, the luminal ER-positive groups, and a HER2 overexpressing group.