ERBB3 and neoplasm: Patritumab deruxtecan (HER3-DXd) is a HER3-directed ADC composed of a monoclonal antibody to HER3 covalently linked to a topoisomerase I inhibitor payload with a DAR ratio of 8 and is cell membrane-permeable, thus allowing cell death both at the target and surrounding tumor cells (43) (Figure 1).