[Mucinous tubular and spindle-cell carcinoma of the kidney]

4 cases (2 males and 2 females) of mucinous tubular and spindle-cell carcinoma of the kidney were studied. The patients' age was 43 to 87 years. Microscopically, this tumor comprised two major cell populations. One of them involved spindle cells with a sparse cytoplasm, which were arranged in the fascicular pattern, often resembling low-grade smooth muscle tumors. The other population was small cuboidal cells with round nuclei and an eosinophilic cytoplasm. The mitotic activity was low. Only one tumor had both cell components. The other three tumors were represented by the second type cells. Immunohistochemical staining with avidin-biotin was performed by using cytokeratin, vimentin, SMA, p53, Bcl 2, EMA, and CD10. All cases were stained positively with antibodies to the cytokeratins AE1-AE2 and vimentin. The expression of EMA, Bcl 2, and CK7 was varying in different tumors. Responses to smooth muscle actin, p53, CK20, and CD10 were negative in all cases. Mucinous tubular and spindle-cell carcinoma of the kidney should be differentiated from angiomyolipoma with the preponderance of a leiomyomatous component, renal smooth muscle neoplasms, metanephrotic adenoma, and renal cell carcinoma with sarcomatoid differentiation.