Sarcomatoid renal tumors. Clinicopathologic correlation of three cases.

The clinical, light and ultrastructural features of three renal neoplasms demonstrating a sarcomatous appearance on light microscopic examination are reported. At the time of radical nephrectomy, all three tumors displayed aggressive features with capsular invasion and either metastases or invasion of adjacent organs. Ultrastructural examination revealed epithelial features in a pure spindle cell tumor and in a malignant fibrous histiocytoma-like tumor (sarcomatoid renal carcinoma) and smooth muscle differentiation (leiomyosarcoma) in a lesion showing features of malignant fibrous histiocytoma. All three patients died from 1 to 9 months after nephrectomy. Renal tumors with a sarcomatous histologic appearance are aggressive neoplasms that cannot be classified accurately solely by employing light microscopic criteria.