Solitary Fibrous Tumor of the Kidney: A Wide Spectrum of an Uncommon Entity from Benignity to Malignant Metastatic Disease

Solitary fibrous tumour (SFT) is a spindle cell neoplasm that rarely occurs in the kidney. It has been reported mainly in the pleura, but it can also arise from almost every organ. Benign SFT of the kidney has been described in several cases, even with metastatic lesions, but only seven cases of malignant SFT including this case have been documented; and only three cases out of seven had distant metastasis. Clinical features are indistinguishable from other renal neoplasms. Diagnosis is based on inmunohistochemical analysis, showing positive staining for CD34, as a key for diagnosis. We report two different cases, with very different behaviour; showing the wide spectrum of malignancy of this entity; with a comprehensive review of the literature.