Tzm deruxtecan (formerly DS-8201), an antibody-drug conjugate consisting of a humanized anti-Her2 monoclonal antibody linked to a topoisomerase I inhibitor payload through a tetrapeptide-based cleavable linker (drug-to-antibody ratio, 8:1), can also effectively target tumor cells that express low levels of Her2 and can deliver its potent cytotoxic payload through the bystander effect to neighboring tumor cells heterogeneously expressing Her2 [21]. The gene discussed is ERBB2; the disease is neoplasm.