Solitary fibrous tumor of the kidney with massive retroperitoneal recurrence. A case presentation.

Solitary fibrous tumor is an unusual spindle cell neoplasm that usually occurs in the pleura but has also been described in other sites. Renal presentation is rare and only 38 cases of SFT of the kidney have been described until now. Up to 90% of the tumors have benign characteristics. Local retroperitoneal recurrence is extremely rare. We report a case of a large malignant solitary fibrous tumor recurrence after the surgical excision of the primary tumor. Histological examination of the specimen confirmed the diagnosis by revealing highly positive reaction of the neoplasmatic cells for vimentin, CD34, bcl-2 and moderately positive for actin. The rate of Ki67 lied between 2-7%. No adjuvant therapy was given to the patient and he is disease-free with no imaging findings of recurrence or metastasis 9 months after the re-operation.