Background
Trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) are antibody-drug conjugates (ADCs) increasingly used in HER2-negative breast cancer. We hypothesized that treatment benefit would vary across HER2-null, HER2-ultra-low, and HER2-low subgroups of HER2-negative breast cancer patients. We also aimed to study the clinical impact of different sequencing of the two ADCs.