Abstract: Objective To explore the clinical features, histopathologic manifestations and treatment methods of giant congenital melanocytic nevi （GCMN）. Methods The clinic data of 20 GCMN patients were collected and analyzed. The biopsy specimens were obtained for HE, Masson and immunohistochemical （HMB-45, Melan-A, PCNA） staining and were observed under light microscopy. Results All of these cases were sporadic cases and patients were all born with GCMN. The most common lesions were head and face, hindquarters cadres and arms. Typical lesions for GCMN were large-area lesions, with color of light brown to dark black, and covered with hairs （mostly black thick hair）. Histologically, GCMN contained nevus cells within deep dermis and even in subcutaneous tissue. The phenomenon of “Grenz zone” and “pigment incontinence” could be observed in the superficial layer of dermis. For immunohistochemical staining, the expression of Melan-A and S-100 were positive in the nevus cells of GCMN, and HMB-45 was focal positive. Positive PCNA staining showed high proliferation state of nevus cells. In history observation after non-surgical treatment, a lot of nevus cells in the superficial layer of dermis were killed while deep nevus cells uninvolved after chemical peeling. After laser treatment, the dermal papilla layer pigmentation disappeared, so the pigment appearance could be partly improved. Conclusion Nevus cells infiltrate deeper in GCMN. Nevus cells in GCMN and melanin cells homologous may have same ancestor and are in highly proliferation state. Chemical peeling treatment and laser therapy, which are regarded as superficial and conservative treatments, both have their unique characteristics. While all of them can only partly improve local appearance and failed to cure. In GCMN which involves large area of body, treatment is still difficult, and new strategies still need to be explored.

Key words: Congenital giant melanocytic nevi, Histopathology, Treatment