Sarcomatoid renal cell carcinoma: the chromophobe connection.

Eleven cases of sarcomatoid renal cell carcinoma were studied to determine the relative frequency of various subtypes of renal cell carcinoma that may be associated with sarcomatoid transformation. The epithelial components in these tumors were subcategorized according to established histologic criteria into chromophobe carcinoma (n = 6 cases), clear cell carcinoma (n = 3), papillary carcinoma (n = 1), and indeterminate (n = 1). In nine cases, material was available for immunohistochemical and DNA ploidy studies. The sarcomatoid component in all cases showed positivity for epithelial membrane antigen cytokeratin, indicating an epithelial derivation of these cells. Staining for mesenchymal markers was mostly negative, except for vimentin, which reacted strongly in all cases. DNA ploidy studies using flow cytometry and cell image analysis provided very similar results. Five of five chromophobe sarcomatoid carcinomas showed hypodiploid cell lines in the epithelial areas, whereas the sarcomatoid components mostly showed aneuploid peaks. In the remaining cases, DNA ploidy pattern was more variable. These findings indicate that chromophobe carcinoma may be the most frequent epithelial component associated with sarcomatoid renal cell carcinoma.