DLL1 and breast cancer: To investigate the clinical significance of DLL1 in breast cancer, we assessed DLL1 protein expression by performing IHC on primary human patient samples (TNBC patients n = 58, non-TNBC patients n = 60, and adjacent normal tissue n = 23) using an anti-DLL1 antibody (Fig. 1a, b and Supplementary Table S1A).