Genes commonly found to be transcriptionally silenced due to promoter hypermethylation include: Cyclin-dependent kinase inhibitor p16, a cell-cycle inhibitor; MGMT, a DNA repair gene; APC, a cell cycle regulator; MLH1, a DNA-repair gene; and BRCA1, another DNA-repair gene.[9][11] Indeed, cancer cells can become addicted to the transcriptional silencing, due to promoter hypermethylation, of some key tumor suppressor genes, a process known as epigenetic addiction.[12]