HER2-directed antibody–drug conjugate in which a humanized anti‑HER2 antibody is linked via a protease-cleavable vedotin linker to the microtubule inhibitor MMAE. Binding to HER2 triggers internalization and lysosomal release of MMAE, which inhibits tubulin polymerization, causing G2/M arrest and apoptosis, with potential bystander cytotoxicity to adjacent cells.