TOP2A and laryngeal carcinoma: Elimination of methylation of TOP2A by treatment with the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, not only sensitized resistant laryngeal cancer cells to radiotherapy, but re-activated expression of these genes, clearly supporting the theory that changes in DNA methylation levels contribute to radioresistance of laryngeal squamous cell carcinoma [45].