Melanocytic Nevi in Malignant Melanomas

Abstract

Background: A substantial proportion of malignant melanomas arise in preexisting melanocytic nevi. However, the clinical and dermoscopic features of such combination lesions have not been well defined in the literature. Objective: To determine the ability to recognize in thin malignant melanomas the presence or absence of melanocytic nevi based on clinical and/or dermoscopic observations. Methods: Thirty malignant melanomas, less than 1 mm in Breslow thickness, were studied clinically, dermoscopically, and histologically for the presence or absence of features of a melanocytic nevus. Results: The ability to recognize melanocytic nevi within thin malignant melanomas was poor by clinical and dermoscopic examinations, with 30% false negatives and 23% false positives. Conclusion: One cannot depend on clinical and/or dermoscopic observations to rule out a melanocytic nevus within a thin malignant melanoma. Histopathologic study of a small portion of a combined melanocytic neoplasm could lead to the mistaken conclusion that the lesion is entirely a melanocytic nevus or entirely a malignant melanoma. Therefore, when feasible, lesions suspected of being malignant melanomas should be totally excised and step-sectioned throughout.