Data suggested that cancer appears to be a process that is fuelled both by genetic alterations and by epigenetic mechanisms. Epigenetics refer to the study of changes in gene expression that can be mitotically inherited, but is not associated with the changes in the coding sequence of the affected genes. The DNA methylation in the promoter regions is a powerful epigenetic mechanism for the suppression of gene activity.Hypomethylation and hypermethylation are the two kinds of methylation defect that is observed in a wide variety of malignancies. Hypomethylation is common in solid tumors such as metastatic hepatocellular cancer, in cervical cancer, prostate tumors, and also in hematologicalmalignancies such as B-cell chronic lymphocytic leukemia. A large number of genes involving fundamental cellular pathways may be affected by aberrant CpG island methylation in association with transcriptional silencing in virtually all tumor types.