ERBB2 and breast cancer: Now, Trastuzumab deruxtecan (T-DXd, formerly DS-8201) is a highly effective HER2-targeted antibody drug conjugate (ADC) with a topoisomerase I inhibitor payload, which is the first choice in advanced HER2-positive breast cancer for second-line treatment recommended by 2021 ESMO Clinical Practice Guideline (34) and 2022 ASCO Guideline Update (35).