Large congenital melanocytic nevi and the risk for development of malignant melanoma and neurocutaneous melanocytosis.

OBJECTIVE: To determine the risk for developing malignant melanoma and neurocutaneous melanocytosis (NCM) in patients with large congenital melanocytic nevi.

DESIGN: Follow-up data suitable for calculations were available on 160 patients in the New York University Registry of Large Congenital Melanocytic Nevi who had been free of known melanomas or NCM when entered into the Registry. The cumulative 5-year life-table risks for developing melanoma and NCM were calculated. The relative risk for developing melanoma, using a control general population reference group, was determined.

RESULTS: The 160 patients (median age at entry: 14 months) were followed prospectively for an average of 5.5 years. Three extracutaneous melanomas developed: 2 were in the central nervous system (CNS) and 1 was retroperitoneal. The 5-year cumulative life-table risk for developing melanoma was 2.3% (95% confidence interval [CI]:.8-6.6) and the relative risk was 101 (95% CI: 21-296). No melanoma occurred within a large congenital melanocytic nevus. Four patients developed manifest NCM, 2 with CNS melanomas. The 5-year cumulative life-table risk for developing NCM was 2.5% (95% CI:.8-7.2). Ten patients were excluded from the calculations because of preexisting disease on entry into the Registry: 5 with manifest NCM and 5 with melanomas (3 in large congenital melanocytic nevi, 1 in nonnevus skin, and 1 unknown primary).

CONCLUSIONS: Patients with large congenital melanocytic nevi are at increased risk for developing melanomas. There is also a significant increased risk for developing NCM. The high incidence of CNS involvement may influence decisions concerning treatment of the large congenital melanocytic nevi.