Monoclonal antibodies against human epidermal growth factor receptor 2 (HER2; also known as ErbB2), e.g., trastuzumab and pertuzumab, are widely used in HER2-positive breast cancer and more recently also in other HER2-positive cancer types such as gastro-intestinal tumours [38,39,40]. This evidence concerns the gene ERBB2 and digestive system neoplasm.