ERBB2 and breast cancer: Since the approval of trastuzumab, the first anti-HER2 agent (34) for BC treatment in 1998, an array of other anti-HER2 agents, such as pertuzumab, lapatinib, T-DM1, and trastuzumab- Deruxtecan (T-Dxd) mAb-drug conjugates (ADCs) and others have been approved, significantly improving the outcome of BC patients (Figure 2).