EXTRAPLEURAL SOLITARY FIBROUS TUMOR - A REPORT OF 7 CASES

Solitary fibrous tumors (SFTs) are rare, spindle-cell neoplasms genera lly associated with the serosal surface, especially the pleura. Histop athologic, immunohistochemical, ultrastructural, and now cytometric an alyses were performed on seven SFTs of extrapleural sites (two retrope ritoneal, two soft tissue, one each peritoneal, nasal cavity, and orbi t). Five patients were women, and two were men, aged from 21 to 68 yea rs (average, 39 yr), All of the lesions presented as well-circumscribe d masses. The lesions ranged in size from 2 to 20 cm in greatest diame ter. Histologically, these lesions were entirely comparable to the ple ural SFTs and lacked the characteristic features of other recognized n eoplasms that occur in these regions. One tumor contained pleomorphic and round-cell sarcomatous foci. Immunohistochemically, all of the tum ors were strongly positive for vimentin and CD34. Six of the seven tum ors showed varying numbers of spindle cells positive for alpha smooth muscle actin, HHF35, neuron-specific enolase, Leu 7, or glial fibrilla ry acidic protein. Ultrastructural examinations of three tumors showed that they were composed of primitive mesenchymal or fibroblast-like c ells. Six tumors examined were diploid by now cytometric examination, Clinical follow-up in six patients ranged from 1 to 7.5 years (average , 2.6 yr) and showed that five patients remained well with no evidence of disease after excision and that the patient with the sarcomatous e lements died of recurrence 2.5 years after surgical treatment. These f indings suggest that SFTs represent ubiquitous neoplasms of fibroblast s or primitive mesenchymal cells with aggressive potential.