MAPK signaling promotes cell growth and survival and is constitutively active in nevi. RAS family members are activated by receptor tyrosine kinases and signal through effector proteins, including RAF kinases and PI3K. Acquired melanocytic nevi harbor oncogenic mutations in BRAF, which is the predominant oncogene associated with melanoma. Congenital melanocytic nevi, blue nevi, and Spitz nevi frequently harbor NRAS mutations, GNAQ mutations, and HRAS alterations, respectively (Modified from N Engl J Med. 2010 Sep 30;363(14):1352-60 Copyright © (2010) Massachusetts Medical Society. Reprinted with permission.)