The ADC trastuzumab deruxtecan (T-DXd) has shown the most significant activity in HER2-low metastatic BC, with a 37% response rate and 11-month PFS in heavily pretreated patients.38 T-DXd also demonstrated longer PFS and OS compared to the physician’s choice of chemotherapy.39 In the phase 3 DESTINY-Breast04 and DESTINY-Breast06 trials T-DXd significantly improved PFS in HR+/HER2-low and HR+/HER2-ultralow advanced BC patients. Here, ERBB2 is linked to breast cancer.