ERBB2 and neoplasm: Examples include the first anti-HER2-targeted ADCs (trastuzumab emtansine (T-DM1)), linking a cleavable linker to the HER2-targeting mAb trastuzumab and combining it with DM1, and trastuzumab deruxtecan (T-DXd), incorporating a potent topoisomerase-I inhibitor payload linked by a cleavable linker, which exhibits superior efficacy in tumours expressing low or heterogeneous levels of HER2 that attributes to its bystander effect.