DNMT1 is the major DNA-methyl-transferase responsible for the maintenance of DNA methylation after DNA replication; by contrast, DNMT3a and DNMT3b are de novo methyl-transferases that are often dysregulated in many types of tumors, such as colon, breast and pancreatic cancers, thus representing a therapeutic target [26]. This evidence concerns the gene DNMT3A and familial pancreatic carcinoma.