Thickness of Melanocytes in Giant Congenital Melanocytic Nevus for Complete Surgical Excision: Clinicopathological Evaluation of 117 Lesions according to the Area and Size

Background: Giant congenital melanocytic nevi (GCMN) are usually defined as nevi that exceed 20 cm in maximal diameter or 15% of the total body surface area. There have been reports of life-long malignant change risks arising from GCMN, leading to surgical excision of GCMN. Objective: To evaluate the thickness of melanocytes according to the clinical factors of the patients to provide objective information for complete resection of the lesion. Methods: Overall, 75 patients diagnosed with GCMN between 2000 and 2021 were included, and their clinical records were collected retrospectively. 117 pathologic slides obtained during excision were reviewed to measure nevus thickness. Clinical factors were assessed with a generalized estimated equation model for association with nevus thickness. Results: The thickness of nevus was significantly associated with the location and size. Nevus thickness was more superficial in the distal extremity than in the head and trunk (P = 0.003 [head]; P < 0.001 [trunk]; P = 0.091 [Proximal extremity]). A nevus over 60 cm was deeper than 20–29.9 cm (P = 0.035). An interaction between size and location existed (P < 0.001). Conclusion: GCMNs have deference in thickness according to location and size. Therefore, it is necessary to devise an approach optimized for each patient to treat GCMN.