ERBB2 and breast neoplasm: While some antibodies already address this issue by inhibiting heterodimer formation rather than individual receptors or homodimers, it should be noted that trastuzumab has been shown to exert preferential activity in breast tumors driven by HER2 homodimers [51], while it is unable to block ligand-induced formation of HER1/HER2 or HER2/HER3 heterodimerization [52,53].