(2) The bivalent binding to HER2 in our BsAb maintains high avidity (Fig. 1B) so as to maximize tumor binding, while the monovalent binding to HER2 (either heterodimeric bispecific IgG or trastuzumab-Fab) is 10-fold lower than trastuzumab.16 Here, ERBB2 is linked to neoplasm.