Extrapleural Solitary Fibrous Tumor A clinical & pathological study of 8 cases

ABSTRACT

We reviewed eight solitary fibrous tumors occurring at sites other than pleura (three orbit, two retroperitoneum, one each hard palate, thyroid, and tongue) which shared the histologic and immunohistochemical features of solitary fibrous tumors of pleura. Six patients were women, and two were men, aged from 26 to 74 years. The tumors ranging from 1.5 to 19 cm in diameter presented as well-circumscribed, unencapsulated, soft to rubbery tissue masses. Histologically they were characterized by a proliferation of spindle or ovoid cells intervened by a dense bundles of collagen. A variety of growth patterns was identified but the so-called patternless pattern was the predominant one. One tumor exhibited highly cellular sarcomatous areas with extensive necrosis, which was diagnosed as malignant solitary fibrous tumor. Immunohistochemical studies showed that all of the tumors were strongly positive for both CD34 and vimentin, but negative for cytokeratin, S-100 protein, EMA, and desmin. One case examined ultrastructurally showed features of fibroblast. All but one showed no evidence of recurrence or metastasis over follow-up period of 14 to 32 months. We conclude that extrapleural solitary fibrous tumors represent a distinct mesenchymal tumor with variable histologic features and should be differentiated from other spindle cell mesenchymal tumors.