The use of trastuzumab is indicated for metastatic gastric cancer with HER2 overexpression (defined as immunohistochemistry [IHC] staining pattern 3 +, or IHC2 + and in-situ hybridization [ISH] +) based on a proven survival benefit (Bang et al. 2010; Moehler et al. 2011). Here, ERBB2 is linked to gastric cancer.