Disitamab vedotin (RC48) is a HER2-targeted antibody–drug conjugate that binds HER2 on tumor cells and is internalized. A cathepsin-cleavable linker releases the payload MMAE inside lysosomes, leading to microtubule depolymerization, G2/M cell-cycle arrest, and apoptotic cell death; the membrane-permeable MMAE can also cause a bystander effect. Fc effector functions may contribute.