Abstract

Although the liposarcoma is a common malignant mesenchymal tumor of the retroperitoneum, its occurrence in the kidney is very rare. A few cases involving only the renal parenchyma have been reported. The histologic features of these cases are not different from those of other body sites. We report a case of pleomorphic liposarcoma arising in the kidney of a 36-year-old man. He had been suffering from pain in the right flank for two weeks. A computed tomographic scan demonstrated a large mass in the right kidney. He underwent a radical nephrectomy under the clinical impression of renal cell carcinoma. There was a 11 cm-sized well demarcated solid mass in the lower pole of the right kidney. Microscopically, the tumor consisted of pleomorphic spindle and epithelioid cells with focal areas showing distinct adipocytic differentiation and geographic necrosis. A few diagnostic lipoblasts were present. Despite extensive search on samples, no carcinomatous component was found. Immunohistochemically, all of the tumor cells were negative for cytokeratin but positive for vimentin. Lipoblasts were positive for S-100 protein as well as for vimentin. When the kidney tumor is exclusively sarcomatous, a generous sampling with proper immunohistochemical staining is recommended to differentiate a primary sarcoma of the kidney from a sarcomatoid carcinoma.