ERBB2 and breast cancer: Trastuzumab, an anti-HER2 extracellular domain IV binding antibody, significantly improves long-term prognosis in HER2-positive BC patients; pertuzumab, an antibody that binds to HER2 extracellular domain II, has demonstrated promising efficacy in both metastatic and early BC and is an integral part of HER2-positive BC therapy [1, 2].