Perturbation of DNA methylation and demethylation by carcinogens during early stages of cancer development. DNA methylation patterns are dynamically balanced by methylation and demethylation processes. Exposure of cells to carcinogens could lead to transcriptional remodeling and histone mark switches at key genes through signaling pathways. The promoter regions of these genes lose 5mC and gain 5hmC at the early stages of exposure, perhaps due to activated demethylation, and these changes ultimately lead to the aberrant methylation pattern seen in cancer. 5caC, 5-carboxylcytosine; 5fC, 5-formylcytosine; 5hmC, 5-hydroxymethylcytosine; 5mC, 5-methylcytosine; DNMTi, DNA methyltransferase inhibitor; HDACi, histone deacetylase inhibitor.