ERBB2 and metastatic malignant neoplasm: In addition to anti-HER2 agents, new treatments for HER2+ disease have been tested in the clinic such as Trastuzumab deruxtecan (T-DXd), a HER2 antibody-drug conjugate (ADCs), which is composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a topoisomerase I inhibitor payload, and have led to remarkable responses in previously treated HER2+ metastatic cancer.