ERBB2 and Decreased total neutrophil count: In this network meta-analysis of treatment after progression on a CDK4/6i in patients with ER + MBC, we found that in HER2-low tumors, trastuzumab deruxtecan and sacituzumab govitecan showed similar efficacy (PFS and OS), with higher toxicity for sacituzumab govitecan, driven by neutropenia and diarrhea.