MELANOMA MIMICKING DERMAL AND SPITZS NEVUS (NEVOID MELANOMA)

We describe two examples of malignant melanoma that present with clini cal and histopathologic characteristics resembling the benign acquired dermal nevus and the spindle and epithelioid cell nevus (Spitz's nevu s), respectively. Both lesions were present on the trunk of adult pati ents. The clinical impression in both cases was dermal nevus. Histopat hologically, these lesions were fairly well circumscribed and symmetri cal; they exhibited an expansile dermal proliferation of atypical nevo melanocytes in nests and fascicles with only minimal intraepidermal in volvement. These lesions which we will designate as ''nevoid'' melanom a can be misinterpreted as benign nevi because of the absence of promi nent intraepidermal pagetoid spread and the pattern of apparent dermal maturation at the base of the tumor associated with a gradual diminut ion of cell size. These features mimic the maturation phenomena in ban al dermal nevi and spindle and epithelioid cell nevi. The differential diagnosis includes other types of melanoma, and various benign entiti es characterized by a predominantly dermal proliferative process, such as deep penetrating nevus and cellular neurothekeoma. The recognition of nevoid melanoma is critical so that patients with these lesions re ceive appropriate therapy for malignant melanoma.