ERBB2 and breast cancer: Trastuzumab is a humanized anti-HER2 antibody and it is the first HER2-targeted therapeutic monoclonal antibody approved by the United States Food and Drug Administration (FDA) in 1998 for the therapy of metastatic HER2-positive breast cancer and in 2010 for the therapy of HER2-positive metastatic gastroesophageal junction and gastric cancer4,5.