ERBB2 and breast carcinoma: Results from the DESTINY-Breast04 and DAISY trials generated interest in accurate identification of HER2-low breast cancers.1,11 The DAISY trial included a cohort of metastatic breast cancers that were HER2-negative n = 38, IHC 0/FISH negative and were treated with T-DXd, 23% of these patients experienced tumor response.11 This unexpected result is attributed to false negative IHC staining and demonstrates the limitation of IHC to select patients for T-DXd therapy.