Trastuzumab (Herceptin®) is a humanized IgG1 monoclonal antibody approved for the treatment of early HER-2 positive breast cancer, as adjuvant and neoadjuvant therapy, and for the treatment of metastatic HER-2 positive gastric adenocarcinoma of esophagogastric junction disease [20]. This evidence concerns the gene ERBB2 and gastric adenocarcinoma.