The pathogenesis of cancer includes both genetic and epigenetic mechanisms. The term <<epigenetic>> refers to any alteration of gene expression, potentially hereditary, which is not accompanied by a modification in the DNA sequence. The effects of epigenetic changes include alteration of DNA transcription, aberrant activation of specific genes, predisposition of genetic instability through alteration of the control of chromosome replication and silencing of the genes implicated in cancer initiation and progression. Among the various epigenetic alterations that lead to altered gene expression, methylation is the main epigenomic mechanism implicated in cancer, whether through a phenomenon of overall hypomethylation or hypermethylation localized in the promoters of specific genes.