Epigenetic alterations such as DNA methylation and histone modification play a role in gene silencing in tumorigenesis. DNA methylation affects the expression of genes involved in cell cycle checkpoint, apoptosis, and DNA repair. Recently, epigenetic alterations are shown to play a role in silencing microRNA. Mutations of DNA methyltransferase and histone modification enzymes such as DNMT3A, UTX and EZH2 have been shown in various types of tumors. Genes involved in epigenetic regulation may be novel targets of cancer therapy in the near future.