Compared to T-DM1, T-DXd has a higher antibody to drug ratio (8 versus (vs.)3–4) and is probably more potent than T-DM1 as a result of the properties of its payload that facilitates penetration of deruxtecan through the cell membrane of the HER2+ tumor cells or neighboring cells, without requiring high HER2 expression levels [22,81]. This evidence concerns the gene ERBB2 and neoplasm.