Ossifying fibromyxoid tumor of soft parts: Clinicopathologic, immunohistochemical and ultrastructural study of four cases

Four cases of uncommon soft tissue tumors were investigated histopathologic ally. All of them consisted of fibrous and myxoid components, and mature bo ne showed shell-like characteristics. Histological features revealed these tumors were well circumscribed by a thick collagenous fibrous capsule and c omposed of uniform-sized fusiform cells with eosinophilic cytoplasm and a r ound or oval nucleus in the myxoid matrix. An incomplete shell of mature bo ne with lamellar structure was also observed at the periphery. Immunohistoc hemical and ultrastructural studies were performed. The major component of the proliferating cells in the tumors had positive staining for vimentin, S -100 protein, neuron-specific enolase and synaptophysin. The myxoid matrix was stained by alcian blue and was digested completely by pretreatment with hyaluronidase. Electron microscopy showed the cytoplasm contained dense-co re granules measuring 100-200 nm and abundant filaments of an intermediate size. It is suggested that these uncommon tumors might be diagnosed as the 'ossifying fibromyxoid tumor of soft parts' previously described by Enzinge r et at, which were derived from peripheral nerve sheath tumors such as neu rofibroma and myxoid neurofibroma.