CDKN2A and brain cancer: The low expression of ARF mRNA is frequently observed in human cancers and is usually caused by hyper-methylation on the CpG island of the ARF promoter or deletion of the genetic region and has been described in breast, bladder, colon, liver, gastric, lung, oral, prostate and brain cancers and has emerged as a predictor of poor prognosis in breast, head and neck, colon and bladder carcinomas [82].