Pertuzumab (PER), another anti-HER2 antibody, binds to domain II of HER2 in HER2-positive breast cancer cells; its MOAs include inhibition of ligand-dependent HER2–HER3 signaling by blocking heterodimerization of HER2 with other HER family members (including epidermal growth factor receptor [EGFR], HER3, and HER4) and ADCC [6, 7]. Here, ERBB3 is linked to breast cancer.