ERBB2 and neoplasm: Trastuzumab emtansine (Trastuzumab-DM1) is a new product in which the Trastuzumab moiety binds to HER2 on tumor cell surfaces and, upon internalization, the DM1 moiety is released and binds to tubulin, thereby disrupting microtubule assembly/disassembly dynamics and inhibiting cell division and proliferation.