For example, trastuzumab, an anti-HER2 monoclonal antibody, improved overall survival in HER2 metastatic9 and early breast cancer.10-12 Additional anti-HER2 agents were further approved on the basis of outcome improvement, including small molecule inhibitors (eg, neratinib13), antibodies (eg, pertuzumab14,15), and antibody-drug conjugate (eg, trastuzumab emtansine16,17 and trastuzumab deruxtecan18). This evidence concerns the gene ERBB2 and breast cancer.