NRAS and melanoma: In this regard, mutations in the upstream gene NRAS which occur in about 15% of cutaneous melanomas (NRAS and BRAF mutations are mutually exclusive in the same tumor, suggesting functional redundancy [5,54]), have been rarely found in melanoma lesions arising in sun-exposed sites; they do not correlate with the degree of sun exposure, histologic subtype, or anatomical site [55,56].