ERBB2 and gastric cancer: HER2 gene amplification or protein overexpression (i.e., tumors scored 3+ by IHC), account for about 10% to 22% of gastric cancer (GC) and represent a requisite for the addition of trastuzumab (anti-HER2) to first-line chemotherapy in unresectable or metastatic GC (mGC) since its addition increased survival from 11.1 to 13.8 months versus chemotherapy alone [1].