HER2 amplification and mutations have emerged as oncogenic drivers and therapeutic targets not limited to breast and gastric cancer, but also in a variety of cancers[12] such as lung,[13] colorectal,[14] bladder,[15] and biliary,[16] urothelial carcinoma,[17] gynecologic,[18] and head and neck cancers.[19] Even if an actionable gene mutation is found in these cancers, the incidence of HER2 amplification is less than 5%.[4] Despite its considerable therapeutic potential, the evidence is not matured yet to use the treatment in routine clinical practice. This evidence concerns the gene ERBB2 and gastric cancer.