Some of the key characteristics of this T-DXd include that the HER2 mAB and the payload are conjugated through a cleavable linker; it has a high drug to antibody ratio of 8:1; the cytotoxic payload (deruxtecan, a highly potent topoisomerase I inhibitor) is membrane soluble; and, once released in the HER2+ cell, this molecule can diffuse out of the cell and can have a cytotoxic effect on surrounding HER2-tumor cells and on the tumor microenvironment (TME), a feature defined as the “bystander effect” (Figure 1D) [35]. Here, ERBB2 is linked to neoplasm.