In contrast to breast cancer, a benefit for anti-HER2 targeting therapy seen with trastuzumab in first-line treatment of HER2 positive gastric/GEJ cancer could not be reproduced with other HER2-targeting strategies: no survival benefit was seen with the antibody-drug conjugate trastuzumab emtansine (T-DM1) [14] in second-line, with the tyrosine kinase inhibitor lapatinib in first-line [15] and second-line [16], or with the addition of pertuzumab to trastuzumab and chemotherapy [17] in first-line metastatic HER2 positive gastric/GEJ cancer. This evidence concerns the gene ERBB2 and breast carcinoma.