Trastuzumab (Enhertu) is humanized IgG1 unconjugated antibody, that binds to the extracellular domain IV of a cell membrane-bound glycoprotein Her2, over-represented in 20–30% of breast cancers (Her2-positive cells), which prevents Her2 homo- and hetero-dimerization, required for cell proliferation, angiogenesis, and motility. Here, ERBB2 is linked to breast cancer.