High-level expression of stem cell marker CD133 in clear cell renal cell carcinoma with favorable prognosis.

The cancer stem cell (CSC) model suggests that high levels of CSCs within a tumor are associated with poor prognosis. The aim of this study was to investigate the expression of the stem cell marker CD133 in clear cell renal cell carcinoma (ccRCC), and its prognostic significance. The expression of CD133 was examined in 140 cases of ccRCC using immunohistochemistry. Ki-67 and Oct-4 were double-immunostained with CD133 to evaluate the proliferative activity and the stemness of CD133-expressing cells, respectively. CD133 expression was observed in 45 cases (32.1%) and high levels of expression were found to be associated with a macro-/microcystic pattern, non-sarcomatoid changes and non-metastatic disease. The Ki-67 labeling index tended to be lower in CD133-expressing ccRCCs compared to non-expressing tumors. CD133-expressing tumor cells rarely expressed Oct-4. A high degree of CD133 expression was observed in ccRCC with more differentiated morphology and non-metastatic disease, suggesting that CD133 is a favorable prognostic marker. These results also indicate that CD133 as a single marker may not be sufficient for CSC identification in ccRCC and, therefore, more specific CSC markers should be developed.