SNAI1 and breast cancer: Interestingly, in spite of early NO deficiency (Fig. 3), the onset of functional EndMT in the lungs of 4T1 breast cancer-bearing mice seemed to be delayed until the 3rd week, in spite of the increased expression of Snail transcription factors in the pulmonary endothelium (Fig. 4a–g) and TGF-β1 in the lungs (Fig. 4h) known to drive mesenchymal shift of endothelial cells [22].