[Solitary fibrous tumor: the clinicopathologic and immunohistochemical characteristics of 26 cases].

OBJECTIVE: To study the clinicopathologic and immunohistochemical features of solitary fibrous tumor (SFT) and its biologic behaviour. METHODS: Clinicopathologic data of 26 cases were collected and analyzed. Among them, immunohistochemical staining (Envision method) for CD34, vimentin, CD99, bcl-2, S-100, SMA, HBME-1, EMA and Ki67 were performed in 23 cases. RESULTS: The 17 male and 9 female patients were between 15 and 66 years of age (mean, 44). Their SFTs were located in nose and nasopharynx, cranial cavity, soft tissue, mediastinum, and parietal and visceral pleura. The main clinical manifestations were local mass and pressure symptom. The characteristic microscopic features included patternless growth pattern, alternating hyper- and hypo-cellular areas, blunt spindle cells within keloid-like hyalinization, and hemangiopericytoma-like regions. Positive immunohistochemical staining: vimentin 100%(23/23), CD34 82%(19/23), bcl-2 87%(20/23), CD99 100%(23/23), SMA 30%(7/23). All cases were negative for S-100, HBME-1 and EMA. Follow-up information on 13 cases revealed that 3 patients had had relapse and died, the other 10 patients were alive without evidence of recurrence. CONCLUSION: SFT is a rare mesenchymal spindle cell tumor which may be found in various parts of human body and needs to be distinguished from other spindle cell tumors by differential diagnosis. The immunophenotype can be of help in this connexion. About 10% to 23% SFTs have malignant behaviour, manifesting as local recurrence or metastasis. The behavior of SFT is unpredictable, which requires careful, longterm follow-up.