Two malignant solitary fibrous tumors in one kidney: Case report and review of the literature.

Malignant solitary fibrous tumors of the kidney are very rare. Two tumors in one kidney is particularly rare and has not been previously reported. Due to the non-specific clinical symptoms, it is difficult but also very significant to give a definite diagnosis. Here, we report a case of two renal masses in one kidney. A 56-year-old man was admitted to our hospital complaining of shortness of breath, weakness, hyperhidrosis and intermittent hypoglycemia of 1-year duration without gross hematuria or lumbago. Imaging studies revealed two masses manifesting as inhomogeneous, with soft-tissue density and having no clear boundaries with the kidney. The patient was initially diagnosed with space-occupying lesions of the left kidney (with suspicions of renal cell carcinoma) and left radical nephrectomy was performed. Histologically, the tumors consisted of ovoid or spindle cells, and a hemangiopericytoma-like pattern and cellular atypia was observed in certain areas. Mitotic figures were more than 4 per 10 high-power fields. Immunohistochemically the tumor cells were positive for CD34, CD99 and vimentin. Accordingly, a diagnosis of malignant solitary fibrous tumor of the left kidney (low-grade malignance) was established. Postoperative follow-up of 10 months did not find tumor recurrence or metastasis and hypoglycemia was resolved with the removal of the tumors.