Trastuzumab (Herceptin®, Roche, Basel, Switzerland) is the first humanized monoclonal antibody against human epidermal growth factor receptor 2 (HER2), approved late in 2010 by the U.S. Food and Drug Administration (FDA) in patients with HER2-overexpressing metastatic adenocarcinoma of the stomach or gastro-oesophageal junction (gastric cancer) who have not received prior anti-cancer treatment for the metastatic disease [1]. The gene discussed is ERBB2; the disease is metastatic neoplasm.