This study which addresses the DNA mismatch repair status and colorectal cancer stem cells of 40 right- and 40 left-sided colorectal carcinomas showed that proficient MMR correlated with high levels of CD133-marked putative cancer stem cells in both right- and left-sided tumors, whereas significantly lower levels of CD133-marked putative cancer stem cells were associated with deficient MMR status in colorectal carcinomas found on the right. This evidence concerns the gene PROM1 and colorectal cancer.