Overexpression of the human epidermal growth factor receptor family member HER2, which is also known as erbB-2/neu, is found in approximately 20–30% of breast cancer cases (i.e. HER2-positive breast cancer) and correlates with more aggressive tumor growth, poorer prognosis and reduced overall survival (Tai et al., 2010; Dent et al., 2013; Rimawi et al., 2015). This evidence concerns the gene ERBB2 and breast cancer.