Case of a Giant Conjunctival Melanocytic Nevus

A 78-year-old female experienced extraocular extension of a giant conjunctival melanocytic mass. The clinical diagnosis was conjunctival malignant melanoma. We performed local excision and histopathological examination. The result of hematoxylin-eosin staining disclosed multiple intralesional mucosal cysts and nevus cell nests with abundant melanin. Immunohistochemical examination revealed expression of S-100, melan-A, and HMB-45 and no expression of Ki-67. Histopathological examination showed no evidence of malignancy. Giant conjunctival melanocytic nevi can be diagnostically confused with conjunctival malignant melanoma.