Another first-in-class ADC, trastuzumab deruxtecan (T-Dx) (payload is a topoisomerase I inhibitor), was first approved in 2021; currently, it is approved for HER2-positive breast cancer and, more recently, HER2-low (immunohistochemistry 1+ or 2+) breast cancer, HER2 positive gastric or gastroesophageal cancer, and HER2-mutated non-small cell lung cancer (NSCLC) [5,6,7,8]. Here, ERBB2 is linked to breast cancer.