DNA ligase IV then repairs the breaks and forms a complex with XRCC4 and XLF.11 Previous studies have shown that the expression of many NHEJ-asociated proteins is deregulated in human cancers and helps to predict patient response to radiotherapy.12, 13, 14 Furthermore, the role of the NHEJ proteins in the resistance to IR has been reported both in vitro and in vivo. This evidence concerns the gene LIG4 and cancer.