ANPEP and nonpapillary renal cell carcinoma: Cytoplasmic staining specific for the epithelial cytokeratin and for vimentin, a mesenchymal marker expressed also in the epithelial RCC cells, both in vivo and in vitro [18,25], and specific expression of the proximal tubular marker CD13 were observed in more than 90% of cells, as assessed by immunofluorescence and FACS analysis, according to the proximal tubular origin of ccRCC (Figure 1b).