ERBB2 and breast cancer: Trastuzumab deruxtecan, a drug–antibody conjugate comprising the HER2 antibody trastuzumab with the topoisomerase I inhibitor deruxtecan payload via a synthetic linker, was approved in 2020 by the US Food and Drug administration for application in pretreated patients with HER2-positive BC who showed a poor response to other HER2-targeted therapies [18,19].