Pagetoid melanocytosis: tease or tocsin?

Pagetoid melanocytosis (PM) represents a more precise formulation of the histological phenomenon previously referred to as pagetoid scatter/spread. PM is defined as the upward discontinuous extension of melanocytes into the superficial epidermis. Three histological criteria are presented. PM is a frequent finding in malignant melanoma, occurring in approximately 76% of lesions. PM also occurs in a significant number of certain benign melanocytic lesions: Spitz nevi, nevi of palms and soles, pigmented spindle cell nevi, recurrent nevi, vulvar nevi, and nevi of infancy and childhood. Histological features of PM favoring malignant melanoma over benign melanocytic lesions are a diffuse and dense extension over a wide area, prominent melanocytic atypia, and PM without an underlying junctional melanocytic component (free-floating PM). PM should alert the pathologist to the possibility of melanoma but does not of necessity require a malignant interpretation. The final interpretation of a melanocytic lesion requires evaluation of all the pertinent histological and clinical findings.