PROM1 and renal cell carcinoma: Alternatively, CD133+ cells are very few in the non-SP population of normal kidney as well as in SP and non-SP RCC cells, compared to the SP of the normal kidney (however, CD133 was not present on presumable normal kidney stem cells, isolated by Bruno et al. [76]), pointing the loss of the CD133 marker which could be a very early event in stem cell differentiation and possibly in malignant transformation.