Trastuzumab deruxtecan (T-DXd; DS-8201), a HER2-targeted ADC representing the next generation of improved compounds, has transformed the therapeutic prospect of this class in the treatment of both HER2-low as well as HER2-heterogeneous tumours that had no efficient therapies targeting HER2-expressing cells and allowed to build on safety and preliminary efficacy data provided by T-DM1 [51]. This evidence concerns the gene ERBB2 and neoplasm.