NRAS and melanoma: Melanoma progression has been described as a step-wise transformation of melanocytes to malignant melanoma triggered by a phenotypic switch toward a more aggressive status.24 To determine whether our in vitro model of cellular reprogramming could simulate features of melanoma phenotype switching and the intermediate stages during melanoma progression, we partially reprogrammed Nras-mutated C790 and Braf-mutated 4434 murine melanoma cells for up to 20 days using a lentiviral vector carrying Oct4, Klf4 and Sox2 genes (Fig. 1a, b).