The monoclonal antibody trastuzumab (Herceptin®, Roche) targets Her-2/neu) was successfully introduced in 1998 for first-line (1L) metastatic disease for Her-2-positive breast cancer and in 2010 for Her-2-positive advanced or metastatic gastric or gastroesophageal junction cancer (GC/GEJ cancer) (1–5). This evidence concerns the gene ERBB2 and breast cancer.