NRAS and melanoma: Whilst the MAPK pathway is activated, in melanocytes, by growth factors such as SCF (Stem Cell Factor), EGF (Epidermal Growth Factor), FGF (Fibroblast Growth Factor), or HGF (Hepatocyte Growth Factor), this pathway is very often constitutively activated in melanoma due to the presence of activating mutations of NRAS and BRAF, and inactivating mutations of the GAP NF1. Mutations in NRAS, BRAF, and to a lesser extent NF1, are mutually exclusive because their oncogenic activity is linked to stimulation of the MAPK pathway [31,32].