Primary Leiomyosarcoma of the Kidney: Four Cases

Renal sarcomas are rare tumors. They constitute only 1-2% of malignant renal tumors in adulthood. Leiomyosarcoma is the most common histological type of renal sarcoma (50-60%). Renal leiomyosarcomas are aggressive tumors arising from the renal capsule, renal vein, pelvic musculature or the renal parenchyma. Diagnosis is usually post operative and requires a thorough sampling of the tumor to rule out an epithelial component. We report 4 new cases of primary renal leiomyosarcomas. Typical morphologic pattern shows alternating fascicles of spindle cells with blunt-ended, non-tapering nuclei and eosinophilic cytoplasm. Nuclear pleomprphisim atypia, mitotic figures and necrosis are seen in different ratios. Immunohistochemically the tumor cells of leiomyosarcoma are positive for SMA, desmin, calponin and h-caldesmon and negative for CK, S-100, HMB-45 and CD117. These tumors are classified using the French Federation of Cancer Centers System. To make a diagnosis of a primary renal sarcoma the following criteria should be met: 1) The patient must not have a sarcoma elsewhere to rule out metastasis. 2) Gross must be compatible with origin in the kidney rather than involvement due to retroperitoneal sarcoma. 3) Sarcomatoid renal cell carcinoma must be excluded. They usually have poor prognosis. But small size (<5 cm), low histological grade, absence of lymph node metastases and radical operations are all associated with better prognosis. Despite radical nephrectomy the tumors can run an aggressive clinical course and early local and distant recurrences are common.