In line with the findings that ZEB1 is predominantly expressed in stromal cells but largely absent in epithelial cells, conditional deletion of ZEB1 in mammary epithelial cells (MaECs) did not affect either the development of mammary glands (Supplementary Fig. 3a–c) or the initiation or growth of mammary tumours induced by PyMT oncogene (Supplementary Fig. 3d–h). This evidence concerns the gene ZEB1 and breast cancer.