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[Renal cell carcinoma with a spindle-cell element--sarcomatous or sarcomatoid?].

In this study the light microscopic and electron microscopic findings in two renal cell carcinomas with spindle-cell elements are described. The ultrastructural features of the spindle-cell element of sarcomatoid renal cell carcinoma have previously been documented, namely pentalaminar desmosomes, basal lamina formation and intracytoplasmic lumina with microvilli. The electron microscopic findings in the 2 cases described here showed mesenchymal rather than epithelial differentiation. It would appear that some renal cell carcinomas with a spindle-cell element are true carcinosarcomas, rather than sarcomatoid renal cell carcinoma.