ERBB2 and neoplasm: We now report a BsAb against the HER2 tumor antigen that offers two distinct advantages over the existing technologies: (1) it is based on the fully humanized HER2-specific IgG1 trastuzumab, preserving its pharmacologic advantages17 and bivalent binding to HER2, maximizing tumor avidity; (2) its binding to CD3 is functionally monovalent through the scFv derived from the humanized huOKT3 IgG1 sequence.