Among the number of HER2-directed agents, there is a growing attention towards MT-5111, an immunotoxin whose action is based on the use of a Shiga-like toxin to enter into HER2-positive cells [47]; notably enough, preclinical reports have suggested that MT-5111 could be combined safely with trastuzumab, and MT-5111 is being investigated in breast cancer and GC patients [48]. This evidence concerns the gene ERBB2 and gastric cancer.