OBJECTIVETo study the clinicopathological features and differential diagnoses of mixed epithelial and stromal tumor of the kidney.

METHODSClinical and pathological characteristics of 4 cases of mixed epithelial and stromal tumor of the kidney were studied.

RESULTSThree patients were female and one was male. All patients presented with flank pain and hematuria. Radiologic studies revealed cystic and solid masses involving the kidney. Grossly the tumors had a solid and cyst appearance. Microscopically, the tumors were composed of a mixture of stromal and epithelial elements. The epithelial elements were variable in cell types including cuboidal, hobnail and columnar cells. One case showed Müllerian and intestinal epithelial differentiations. Stromal elements essentially consisted of spindle cells, with thick-walled blood vessels and bands of smooth muscle cells as distinctive features of the tumor. Immunohistochemical staining revealed that the epithelial components were positive for AE1/AE3, whereas the stromal components were positive for ER, PR, and SMA. All patients underwent nephrectomy and were well without evidence of recurrence.

CONCLUSIONSMixed epithelial and stromal tumor of the kidney is a benign neoplasm with distinct histopathological features. It should be distinguished from many other renal neoplasms. Surgical intervention is a preferred therapy.