SOLITARY FIBROUS TUMORS OF SOFT-TISSUE - A CLINICOPATHOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY OF 12 CASES

We describe 12 cases of primary soft tissue neoplasms that showed the histologic and immunohistochemical features of solitary fibrous tumors of serosal surfaces (solitary fibrous mesothelioma, submesothelial fi broma). Nine patients were women and three were men whose ages ranged from 28 to 83 years. Seven lesions were located in the head and neck r egion, and the remainder were located in the back, buttock, perineum, and groin. The lesions measured from 1 to 6 cm in greatest diameter an d presented grossly as well-circumscribed, unencapsulated, soft to rub bery tissue masses, Histologically they were characterized by a prolif eration of spindle cells exhibiting a variety of growth patterns, incl uding storiform, herringbone, neural with wavy nuclei, and hemangioper icytic admired with areas of sclerosis. In two cases the lesions showe d areas of increased cellularity with occasionally scattered mitotic f igures. Three cases were located adjacent to a major salivary gland; i n one, entrapment of normal salivary gland acini and ducts could be ob served at the edges of the lesion. Immunohistochemical studies showed positive staining of the spindle cells with CD34 (anti-HPCA-1) and vim entin antibodies and negative staining with keratin, actin, desmin, S- 100 protein, collagen type IV, and factor VIII related antigen. Follow -up from 6 months to 12 years has shown no evidence of recurrence or m etastasis in any of our patients. Solitary fibrous tumors appear to re present ubiquitous mesenchymal neoplasms that may not be necessarily r estricted to serosal surfaces. Identification of these lesions is of i mportance to avoid misdiagnosis with other more aggressive conditions in soft tissue locations.