Primary renal malignant fibrous histiocytoma is a rare tumor of the kidney. It is clinically and radiologically indistinguishable from a renal cell carcinoma. Even following radical surgery, the tumor shows a strong predilection for local recurrence and the prognosis is generally poor. We report on a 32-year-old man with malignant fibrous histiocytoma of the kidney who remained free of recurrence for 1 year after radical nephrectomy.

Mixed epithelial and stromal tumor of the kidney (MEST) is a rare, recently described benign renal neoplasm that predominantly affects perimenopausal women. It is composed of dual components of epithelial and stromal cells, and the tumor is characterized by admixed cystic and solid growth patterns. Herein, we report on a case of MEST in a 35-year-old woman who presented with an incidentally found renal tumor. The patient has had no evidence of disease 4 years after the surgery. (Korean J Urol 2008;49:174-176)