ABSTRACT
Cancer can be defined in many different ways, depending on the area in which the disease is studied, and it can be understood to encompass a group of about 100 different and distinctive diseases. These diseases are characterized by an abnormal growth of cells that generally lead to an uncontrolled proliferation that, in some cases, can metastasize to other organs and tissues. In healthy cells, while repetitive genomic sequences are heavily methylated, most of the Cytosine–guanine (CpG) islands are unmethylated, which allows genes to be expressed in the presence of the necessary transcriptional activators. Although gene-specific demethylation occurs in the context of global DNA hypomethylation, many of the effects are thought to arise through the activation of the transposable elements and endogenous retroviruses present in the human genome, and through loss of imprinting. The best-studied epigenetic event related to cancer development is probably the hypermethylation of CpG islands associated with the promoter region of tumor-suppressor genes.
