DPP4 and neoplasm: Studies observed the unmethylation of promoter CpG island of EpCAM in tumor tissues including CRC, in comparison to the methylated normal samples, yet it was argued that additional factors are required for its overexpression in CRC [22, 23]; although it is not studied in CRC, higher methylation frequency is linked to ALDH1 suppression in breast cancer, whereas promoter of CD26 is hypermethylated in melanoma cells [24, 25].