ERBB2 and breast carcinoma: The HER2 gene encodes the human epidermal growth factor receptor 2 with tyrosine kinase activity (Slamon et al, 1987) and is overexpressed in 15–20% of breast cancers (Owens et al, 2004), through gene amplification with well correlated level of protein expression (Pauletti et al, 1996; Yarden, 2001).