Congenital nevi less than or equal to 10 cm as precursors to melanoma. 52 cases, a review, and a new conception.

Fifty-two congenital melanocytic nevi (CMN) as precursors to melanoma or severe melanocytic dysplasia were reviewed macroscopically and microscopically. Forty-eight "small" CMN measured less than 10 cm in diameter. Histologically, only five reached to the lower third of the dermis or subcutis ("deep type"); the remaining 47 were limited to the upper two thirds of the corium ("superficial type"). There were 47 invasive melanomas, two in situ melanomas, and three severe focal melanocytic dysplasias. All melanomas were of "epidermal" origin and primarily of the superficial spreading type. The age at diagnosis ranged from 18 to 79 years. Prepubertal melanomas were not observed. Melanoma may also arise on small CMN. The most frequent origin of the melanomas in small CMN and the preferred age at manifestation seem to be different from that for giant nevi.