Multiple melanoma and atypical melanocytic naevi--evidence of an activated and expanded melanocytic system.

Twelve patients with malignant melanoma and/or multiple atypical naevi are described. Of these, three were familial and four were sporadic cases of a syndrome characterized by multiple irregular melanocytic naevi and multiple primary cutaneous malignant melanomata. The other five were cases of multiple atypical naevi without malignant melanoma. Three new features emerge from this study: (1) in these patients malignant melanoma may develop on clinically normal skin; (2) melanocyte counts in normal skin adjacent to the lesion show an expanded population of epidermal melanocytes; (3) most of these patients (9/12) give a history of significant sun exposure. The unsatisfactory terminology previously used in describing this syndrome is discussed, and the term expanded and activated melanocyte syndrome is offered as an alternative.