Ossifying fibromyxoid tumor of soft parts of the back.

We report a first case of ossifying fibromyxoid tumor of soft parts of the back, a 10 x 9.5 x 6 cm well-circumscribed elevated subcutaneous tumor demarcated by an incomplete fibrous capsule with bone formation at its base. The tumor was composed of both myxomatous areas with spindle tumor cells and pseudoalveolar structures with oval tumor cells. The tumor cells had evenly sized, oval nuclei without atypia and slightly eosinophilic cytoplasm with intracellular vacuoles. Immunohistochemical studies revealed positivity for vimentin and focal positivity for S-100 protein. Ultrastructural examination revealed a few filopodia-like processes, discontinuous basal lamina and a few primitive cell junctions. Based on these immunohistochemical and ultrastructural results, this tumor may be related to Schwann's cells. There has been no recurrence 5 years after wide local excision.