Primary malignant melanoma (clear cell sarcoma) of bone: report of a case arising in the ulna.

Background: To the authors' knowledge, there has been no previous report of primary malignant melanoma of bone.

Methods: A 33-year-old woman presented with a tumorous lesion in the olecranon of the right ulna. The histologic diagnosis was malignant melanoma with close similarity to clear cell sarcoma. To exclude the possibility of malignant melanoma metastatic to the bone, clinical investigations including gallium 67-citrate scintigraphy, brain, chest, and abdominal computed tomography, and upper and lower gastrointestinal endoscopic examinations were performed. Conventional histopathologic, immunohistochemical, and electron microscopic studies were also performed.

Results: Clinical investigations showed no lesion suggestive of a primary melanoma other than that in the right ulna. Histologically, the tumor was comprised of polygonal or fusiform cells with clear or granular cytoplasm and vesicular nuclei containing one or two prominent nucleoli. The features were similar to those of clear cell sarcoma (malignant melanoma of soft parts). Fontana preparations and immunohistochemical staining for S-100 protein and HMB-45 (melanoma specific antigen) also revealed that the tumor cells had the characteristics of malignant melanoma. The patient has remained alive and well for more than 5 years after the initial treatment.

Conclusions: The clinicopathologic findings in this case strongly suggested that the lesion was a primary malignant melanoma of bone. Therefore, this is the first report to indicate that malignant melanoma and related diseases can occur even in bone tissue.