Subungual Osteogenic Malignant Melanoma

Abstract

Osteogenic melanoma may mimic many other tumors, especially osteogenic sarcoma; only 12 cases have been reported so far. To characterize this unusual neoplasm further, we present the clinicopathologic findings of a new case. A 67-year-old woman was treated unsuccessfully for “fungal granuloma” of her great toe. After nail ablation and incisional biopsy, the toe was exarticulated. Histologically, we found a high-grade, spindle, focally epithelioid, amelanotic malignant tumor with a distinct osteoid and chondroid matrix. Spindle, epithelioid, osteoblastic, and chondroblastic tumor cells were immunoreactive for vimentin, S-100 protein, and NKI/C3. Ultrastructurally, diagnostic premelanosomes were not identified. Features that support a diagnosis of osteogenic melanoma are superficial subungual location, absence of bone involvement, and immunoreactivity for vimentin, S-100 protein, and NKI/C3. The unusual features of current tumor are absence of radial growth phase, negative reaction to HMB-45, and ultrastructural absence of melanosomes.