Congenital Melanocytic Nevi and the Risk of Malignant Melanoma: Establishing a Guideline for Primary-Care Physicians

Abstract

Objective: The objective of this review is to determine what size congenital melanocytic nevi (CMN) increases the risk of malignant melanoma in affected patients.Background: Congenital melanocytic nevi are benign proliferations of cutaneous melanocytes apparent at birth or in the first postnatal weeks. The Kopf system classifies nevi based on size: small, <1.5 cm in diameter; medium, 1.5–19.9 cm in diameter, and large, ≥20 cm in diameter. Great variability exists in quantifying the risk of malignant transformation from congenital nevi of different sizes. Evidence-based standard guidelines for clinical investigation need to be established. Methods: Literature search included studies on medium, large, and giant congenital nevi in association with melanoma.Results: Three studies pertaining to small, medium, and large congenital nevi are defined. The odds ratio of malignant transformation from small CMN was determined to be 20.9 by history and 10.5 by histology in 238 patients in the case-control study selected. No malignant transformation was found in a prospective study of 230 individuals with medium-sized melanocytic nevi. Finally, a 5% risk of malignant transformation was reported in a prospective study of patients with large congenital nevi.Conclusion: All patients should receive total body skin and mucosal surface exams. Patients with small CMN (<1.5 cm in diameter) and medium CMN (≥1.5 cm–19.9 cm in diameter) should be closely observed over their lifetimes and given the option of specialist referral. Finally, patients with large CMN (≥20 cm in diameter) should be referred to specialists upon initial presentation. More original data and follow-up are needed for maturation of evidence-based clinical recommendations.