The writing and patterning of DNA methylation in mammals is carried out by DNA methyltransferases (DNMTs), in particular DNMT1, DNMT3A and DNMT3B. Recent data show that DNMTs abnormalities are involved in tumor transformation and progression, indicating that epigenetic perturbations caused by DNMTs abnormalities are associated with tumorigenesis [20]. This evidence concerns the gene DNMT3A and neoplasm.