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Kidney fibroxanthoma (malignant fibrous xanthoma): A rare tumor and an unusual cause of retroperitoneal hemorrhage

A case of kidney fibroxanthoma (malignant fibrous xanthoma, malignant variant of xanthogranuloma), a rare malignant neoplasm of kidney, is described. In addition to the typical histologic features of retroperitoneal xanthogranuloma, this tumor showed obvious pleomorphism and mitotic activity of the histiocytes. We present this case in view of the rarity of this neoplasm and the unusual presentation as massive retroperitoneal hemorrhage.