Research on gastric adenocarcinomas, esophageal squamous cell carcinomas, and breast cancer cells has identified a relationship between methylation of the RKIP promoter and low RKIP expression levels, thus suggesting that RKIP can be epigenetically regulated through promoter methylation [161,162,163,164,165,166,167]. This evidence concerns the gene PEBP1 and gastric adenocarcinoma.