Contemporary approach to the classification of renal epithelial tumors.

Our understanding of the morphologic and genetic features of renal epithelial neoplasia has brought about profound changes in the classification of these tumors. It is clear that they represent a heterogeneous group of tumors with distinct histopathologic, genetic, and clinical features ranging from benign to high-grade malignant. "Granular" and "sarcomatoid" carcinomas are not distinct entities, since tumors with granular or spindle cell features may be seen in many tumor-types. Using conventional pathologic tools such as hematoxylin and eosin staining, histochemistry, immunohistochemistry, and electron microscopy, we are able to properly classify the majority of these tumors. Nevertheless, approximately 6% to 7% of cases are impossible to classify in this fashion, thus requiring molecular genetic studies for proper characterization.