T-DXd is composed of an anti-HER2 monoclonal antibody and a topoisomerase I inhibitor (DXd) linked through a cleavable linker, with a drug-to-antibody ratio (DAR) of 8:1, which is much higher than that of traditional ADCs (e.g., T-DM1 has a DAR of 3.5:1), significantly enhancing its cytotoxicity against tumor cells, especially in heterogeneous or low HER2-expressing metastatic lesions (Modi et al., 2020). Here, ERBB2 is linked to neoplasm.