NRAS and large congenital melanocytic nevus: One of the most feared and serious complications associated with large/giant congenital melanocytic nevi is the development of central nervous system involvement, a syndrome referred to as neurocutaneous melanocytosis (NCM), in which the meninges and/or multiple foci of the central nervous system develop melanocytic proliferations (Fig. 6) associated with postzygotic somatic mutations affecting NRAS, which represent the first hit in a multistep oncogenetic process.