List of products in the National Drug Code with proprietary name . Trastuzumab emtansine is used to treat certain types of breast cancer. This medication is used to treat tumors that produce more than the normal amount of a certain substance called HER2 protein. This medication is called a monoclonal antibody and microtubule inhibitor conjugate. Trastuzumab emtansine works by attaching to the HER2 cancer cells and blocking them from dividing and growing. It may also destroy the cancer cells or signal the body (immune system) to destroy the cancer cells. This monograph is about the following trastuzumab emtansine products: trastuzumab emtansine, ado-trastuzumab emtansine.