However, work in colon and brain cancers has revealed that CD133− cells were also able to give rise to tumors suggesting that CD133 positivity as a specific marker for CSCs may not be valid for all solid tumor or sarcoma subtypes (Ogden et al., 2008; Shmelkov et al., 2008; Wang et al., 2008). This evidence concerns the gene PROM1 and sarcoma.