Hiding in plain sight: molecular genetics applied to giant congenital melanocytic nevi.

Large and giant congenital melanocytic nevi are rare malformations that offer surprising insight into prenatal and postnatal acquisition of nevi of any size, central and peripheral nervous system development, and melanomagenesis. In this issue, Charbel et al. demonstrate the use of highly sensitive detection techniques for recurrent but difficult-to-detect mutations in NRAS and BRAF. It is now possible to systematically add a molecular qualifier to distinguish lesions that had once been considered to be equivalent based on the single visual parameter of size. These findings help to elucidate the pathophysiology of congenital melanocytic nevi and their predisposition to malignancy.