CDKN2A and brain cancer: As the ARF promoter contains a CpG island, ARF silencing by hypermethylation of these promoter sequences has frequently been reported in various human cancers, such as breast, bladder, colon, liver, gastric, lung, oral, prostate, and brain cancer [95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110].