GAPDH and colorectal cancer: In this study, 13 genes have been used to test their suitability, including the most broadly-used reference genes Gapdh, Actb, Rplp0, β2m and Hprt, which have been used in normalizing mRNA expression in normal intestinal mucosa, infected intestinal mucosa, intestinal carcinomas, colorectal cancer and different intestinal epithelial processes [23–25].