Reverse transcription-PCR (RT-PCR) analysis of CD133 expression in 32 colorectal cancer cell lines showed positive results in approximately two-thirds of the lines, including COLO 205 cells, and undetectable or low levels of CD133 expression in the remaining, possibly due to gene silencing by promoter hypermethylation of the CD133 CpG island [20]. Here, PROM1 is linked to colorectal cancer.