ERBB2 and neoplasm: In this study, we systemically interrogated the collective role of affinity, avidity and format valence in the ability of a selection of monovalent and bivalent bsAbs composed of the anti-HER2 trastuzumab moiety paired with an array of affinity-modulated variants of the anti-EGFR GA201 mAb to promote selective tumor-targeting under physiological conditions.