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Undifferentiated Pleomorphic Sarcoma (UPS) of the Kidney: Most cases are retroperitoneal in origin with secondary renal involvement. However, rare credible case reports of UPS originating in the kidney have been published. There are no specific criteria for the diagnosis of primary UPS of the kidney; however, there should be no evidence of sarcoma elsewhere in the body (i.e. metastasis should be excluded); the gross appearance should be suggestive of primary renal location; and sarcomatoid renal cell carcinoma as well as other entities such as renal leiomyosarcoma are excluded. This nephrectomy specimen shows a large, fleshy yellow-tan tumor centered in the kidney. Microscopically, it had classic storiform-pleomorphic appearance. Further discussion of UPS is in the Soft Tissue section.