Case of extraskeletal osteosarcoma suspected malignant fibrous histiocytoma.

A case of extraskeletal osteosarcoma, which has been suspected to be malignant fibrous histiocytoma, is reported. The patient was a 62-year old man. He noticed an asymptomatic nodule on his forehead 1 month before the first visit to our clinic. There were 5 firm nodules on his forehead. Wide excision of the lesions and skin grafting was performed. Biopsy specimens revealed dermal and subcutaneous infiltrating tumors without discernible borders, which were composed of spindle-like, histiocyte-like and osteoblast-like cells with pronounced nuclear atypia. In some areas, immature osteoid structures were also found. Immunohistochemical examination revealed that tumor cells react positively with actin, myosin, α1-antitrypsin, S-100 protein, and lysozyme. On the other hand, vimentin, CD34 and factor VIII were negative. Multiple matastatic lesions in the scalp were revealed with a CT scan and MRI. The right-sided hemiplegia was appeared and gradually increased. Therefore, the patient was treated only with anti-edema therapy. He died 3 months after the first visit to our clinic. Compared with osteosarcoma of bone, extraskeletal osteosarcoma is rare. There are 68 cases of this tumor recorded in the Japanese literature.