To determine if the function of Dll1 was specific to the luminal adenocarcinoma MMTV-PyMT model, we crossed the Dll1cKO mice to MMTV-Wnt1 mice, which represents a basal/mixed tumor model29, to generate Wnt1-Dll1cKO mice (Supplementary Fig. 1a). Here, WNT1 is linked to neoplasm.