ERBB2 and neoplasm: Trastuzumab deruxtecan (T-DXd), a novel human epidermal growth factor receptor 2 (HER2)-targeting antibody-drug conjugate is an effective drug in multiple tumour types and has been licensed to treat advanced HER2-positive GOA that has progressed after chemotherapy and trastuzumab and is European Society for Medical Oncology (ESMO) Guideline recommended.