Making a mountain out of a molehill: NRAS, mosaicism, and large congenital nevi.

Linking phenotypic patterns of melanocytic neoplasia to specific gene mutations allows more precise predicting of clinical behavior and response to targeted therapy. In this issue, Kinsler et al. provide evidence that multiple congenital nevi with central nervous system lesions are likely exclusively the result of mosaic mutations in NRAS. We discuss the link between mosaic NRAS mutations, cellular senescence, and clinical phenotype in these nevi.