Cancer cells contain altered DNA methylation patterns. There is much less DNA methylation in cancer cells than in normal cells. At the same time, the promoters of some genes are hypermethylated in cancer cells. These changes are thought to result in stimulation of transcription of the bulk of genes that would be silent in normal cells, while at the same time repression transcription of genes that would regulate normal cellular functions such as DNA repair and cell-cycle control.
Histone modifications are disrupted in cancer cells. Genes that encode histone acetylases, deacetylases, methyltransferases, and demethylases are often mutated or aberrantly expressed in cancer cells. The large numbers of epigenetic abnormalities in tumors have prompted some scientists to speculate that there may be more epigenetic defects in cancer cells than there are gene mutations. In addition, because epigenetic modifications are reversible, it may be possible to treat cancers using epigenetic-based therapies.