A hypothesis incorporating the histologic characteristics of dysplastic nevi into the normal biological development of melanocytic nevi.

A lentiginous pattern of intraepidermal melanocytic hyperplasia, with mild to moderate, random cytologic atypia, forms the conventional basis for the histologic definition of a dysplastic nevus. It is proposed here that these changes actually represent the histologic pattern of a nevus in an active phase of radial growth. The lesser degrees of atypia considered by others to be required for the diagnosis are suggested to overlap changes commonly seen in banal nevi and lentigines. This hypothesis allows the parsimonious concept that a nevus, originating as a lentigo, can at the later sequential junctional, compound, or intradermal stages expand peripherally by a resumption or persistence of the lentiginous pattern of proliferation. The random atypia that is seen in such lesions is suggested to be incidental to the proliferative process rather than indicative of dysplasia as conventionally defined. A familial melanoma-associated phenotype could be accommodated in this model by postulating a heritable defect in mechanisms that control the number or sizes of these hyperplastic lesions.