Is CD133 a biomarker for cancer stem cells of colorectal cancer and brain tumors? A meta-analysis

Background: CD133 has been used to identify normal and cancer stem cells from several different tissues. Nowadays some researchers have reported that CD133 expression was not restricted to cancer stem cells (CSCs) of colorectal cancer and brain tumors, and CD133-negative subsets could also initiate tumors. We therefore performed a meta-analysis to assess the value of CD133 as a biomarker of CSCs for colorectal cancer and brain tumors. Methods: A Medline search was performed to identify relevant studies for the analysis. The meta-analysis was done using RevMan 5.0 software. Outcome measures were colony formation rate and xenotransplanted tumor formation rate. Results: Fifteen identified studies were available for analysis. For in vitro tests, there were no significant differences in the colony formation rates between CD133-positive and CD133-negative cells for colorectal cancer and brain tumors. For in vivo tests, the xenotransplanted tumor formation rate showed a significant difference between CD133-positive cells and CD133-negative cells in colorectal cancer only, corresponding to a risk difference of 0.40 (95%CI: 0.07, 0.73). Samples (cell lines versus tissues), applied biomarkers (combined versus single), and injection site were included as factors in sensitivity analyses, but the results were very inconsistent. Conclusions: CD133 may not be suitable as a universe biomarker in identifying CSCs of colorectal cancer and brain tumors. Additional studies are necessary to further delineate its role.