In HER2-overexpressing breast cancer, T-DXd exhibited an improvement in progression-free survival compared to trastuzumab emtansine (T-DM1), another trastuzumab-based ADC harboring a non-cleavable linker and a maytansine derivative as its payload, in the second-line setting [7,8]. The gene discussed is ERBB2; the disease is breast carcinoma.