GSTP1 and colorectal cancer: It was reported that many genes in colorectal cancer, such as p14, p16, p53, MGMT, APC, hMLH1, THBS1, E-cadherin, TIMP3, and GSTP1, have the presence of promoter CpG island hypermethylation, which is considered to be an early event in colorectal cancer [11, 12].