HER2-targeted antibody–drug conjugate linking a humanized anti‑HER2 monoclonal antibody via a cleavable linker to an exatecan-derived topoisomerase I inhibitor; after HER2 binding and internalization, the linker is cleaved to release the payload, which inhibits Topo I to induce DNA damage, S‑phase arrest, apoptosis, and a bystander cytotoxic effect.