The results of the Trastuzumab for Gastric Cancer (ToGA) Study showed that the prognosis of HER2-positive gastric cancer was improved by chemotherapy with trastuzumab, which is a human epidermal growth factor receptor (HER) 2 antibody to chemotherapy of cytotoxic agent, in combination with fluorouracil (5-FU) and CDDP (2). Here, ERBB2 is linked to gastric cancer.