Image Description
Primary Leiomyosarcoma of Kidney: The differential diagnosis includes sarcomatoid renal cell carcinoma, sarcomatoid urothelial carcinoma, angiomyolipoma, and leiomyoma. Immunohistochemical stains such as keratin are helpful in distinguishing leiomyosarcoma (keratin -ve) from sarcomatoid carcinomas (strongly keratin +ve). The presence of cytologic atypia, increased mitotic activity, and necrosis favor leiomyosarcoma over leiomyoma. Angiomyolipomas are positive for melanocytic markers (HMB45, Melan A) and cathepsin K. One should keep in mind that leiomyosarcoma of the kidney can rarely arise from the smooth muscle component of an angiomyolipoma.