ERBB2 and breast cancer: Combined with recent data showing the activity of anti-HER2 ADCs in HER2-0 BC, such as the DAISY phase 2 trial [43], in which T-DXd achieved an objective response rate of 30% for metastatic HER2-0 BC, it might be worth investigating whether novel quantitative HER2 assays, including those based on mRNA expression and proteomics analyses, may better refine evaluation of HER2 expression and treatment selection for novel ADCs [44].