XRCC6 and nasopharyngeal carcinoma: The Ku70 promoter T-991C (SNP rs5751129) polymorphism is associated with HCC, gastric, oral, renal, and nasopharyngeal cancer susceptibility, and this novel polymorphism is predicted to lead to differential XRCC6 mRNA and Ku70 protein expression levels [115,120,121,122,123].