Xanthogranulomas with inconspicuous foam cells and giant cells mimicking malignant melanoma - A clinical, histologic, and immunohistochemical study of three cases

Histiocytic proliferations can mimic melanocytic tumors and vice versa. The authors describe the clinical, histologic, and immunohistochemical finding s of three predominantly mononuclear xanthogranulomas that were misdiagnose d as malignant melanoma by experienced pathologists. All lesions occurred i n male patients ranging in age from 14 to 75 years. The tumors presented as dermal nodules, two of which were surrounded by an epidermal collarette an d were ulcerated focally. The rumors were composed of a mixed population of large epithelioid and plump spindle cells with pink or pale cytoplasm arra nged in nests and short fascicles. Occasional mononuclear cells had cytopla smic vacuolar changes, but none had well-developed foamy cytoplasm. Rare, m ultinucleated giant cells were present, but they were not of the Touton typ e, Mitotic figures were found in all lesions. Immunohistochemically, most t umor cells (80%-90%) were strongly positive for CD68 and a minority of cell s (10%-15%), located typically at the periphery of the tumor, was positive for factor XIIIa. Two tumors contained rare cells positive for S-100 protei n (5% of tumor cells or less), All tumors were completely negative for tyro sinase (T311), gp100 (HMB-45), and Melan-A (A103), Giant and foam cell-poor variants of juvenile xanthogranuloma have been reported previously, mainly in young children. Their occurrence in adolescents and adults is underreco gnized. Knowledge of this variant is important to avoid misdiagnosing a ben ign tumor as malignant melanoma.