Epigenetic inactivation of RAI2 in primary colorectal cancer. a Representative MSP results of RAI2 methylation status in normal colon mucosa (NC) and colorectal cancer tissues (CRC). b Kaplan-Meier curves show the association of 5-year overall survival (OS) rate and relapse-free survival (RFS) rate of colorectal cancer patients with the methylation status of RAI2. Black, RAI2-unmethylated colorectal cancer patients (n = 110, log-rank test); red, RAI2-methylated colorectal cancer patients (n = 127, log-rank test). c Representative images of RAI2 protein expression in colorectal cancer and adjacent non-tumor tissues determined by IHC (left images, × 100; right images, × 400). d RAI2 expression scores are shown as scatter plots; vertical bars represent the range of data. The expression levels of RAI2 were significantly different between adjacent tissue and colorectal cancer samples (**P < 0.01). The bar diagram shows the expression and DNA methylation status of RAI2 in different cancer samples. Reduced expression of RAI2 was significantly associated with promoter region methylation (**P < 0.01). e TCGA data and GTEx data show RAI2 mRNA expression levels in CRC tissues (n = 383) and normal colorectal mucosa (n = 50) according to RNA-Seq results. Box plots: the levels of RAI2 expression. Horizontal lines: counts of log2 (TPM + 1); TPM, transcripts per million (reads) (***P < 0.001). f RAI2 expression and 5-year OS (n = 333, log-rank test) and RFS (n = 341, log-rank test) from TCGA database for CRC. Kaplan-Meier curves show the association of 5-year OS and 5-year RFS of colorectal cancer patients with RAI2 mRNA expression. Green, RAI2 low-level expression colorectal cancer patients; red, RAI2 high-level expression colorectal cancer patients. g The correlation of methylation of 16 CpG sites around the promoter region and expression of RAI2 (upper panel), and the methylation status of the top three CpG sites (cg06102971, cg06535161) are correlated with loss/reduction of RAI2 expression in 373 cases of CRC (all P < 0.05).