Melanocytic nevi and malignant melanoma.

It has been known for a long time that melanoma can have its origin in congenital or acquired melanocytic nevi. In regard to congenital nevi, there is sufficient evidence to state that large lesions (those greater than 20 cm in diameter) have a significant risk factor that is several-fold greater than for common acquired nevi. Prophylactic excision of such lesions should be strongly considered when it is feasible, but individual circumstances must be taken into account. The risk factors for small and medium-sized congenital nevi have not been accurately determined; therefore, no uniform recommendation can be made regarding their management. There is no objective evidence to indicate that common acquired nevi in any particular anatomic sites, such as volar or genital skin, are at greater risk for the development of melanoma than are any others. Patients with familial dysplastic nevus syndrome must be identified and followed carefully in order to recognize and eradicate evolving and early melanomas. The concept of the sporadic dysplastic nevus syndrome is intriguing and deserves careful study to further define the clinical and histologic diagnostic criteria that will enable accurate determination of its prevalence and risk factors.