NOS3 and breast cancer: Indeed, Smeda et al. (2018) in the same model demonstrated decreased endothelial nitric oxide synthase (eNOS) activity, resulting in a low NO-production state in the pulmonary endothelium during the very early phase of breast cancer pulmonary metastasis, even preceding the onset of its phenotypic switch toward a mesenchymal phenotype (EndMT) (Smeda et al., 2018).