ERBB3 and cancer: These mechanisms include: (1) the synergism due to the different functions of these two antibodies in targeting HER2-positive cancer cells (reviewed in [182]); (2) synergism due to composition-independent inhibitory effects of the combination of the two antibodies in a wide range of HER2/HER3 composition [183]; and (3) synergism of trastuzumab and pertuzumab partly due to the enhanced binding affinity towards the HER2 molecule that originated from the cooperative interactions between the two antibodies [184].