Trastuzumab deruxtecan (T-DXd) is antibody–drug conjugate (ADC), consisting of HER2-specific monoclonal antibody and topoisomerase I inhibitor deruxtecan., with the efficacy in patients with advanced or metastatic HER2-positive or HER2-low BC confirmed in the DESTINY studies program (45–47). The gene discussed is ERBB2; the disease is breast cancer.