CD44 and nonpapillary renal cell carcinoma: Similarly, stem-like cells (variously labelled cancer stem cells, tumour-initiating cells) have also been isolated from ccRCC specimens using a variety of different surface markers, including CD44, Ecto-5′-nucleotidase (CD73), CXCR4, CD105 and aldehyde dehydrogenase 1 (ALDH1) [9–13].