MLH1 and head and neck squamous cell carcinoma: SNPs in several DDR and DNA repair-related genes have been reported to be associated with an increased risk of HNSCC (Table 2), including ERCC1 (67), ERCC2/XPD (67–70), XPC (71, 72) and XPG (69) (involved in NER), APEX1 (73) and XRCC1 (74–76)(involved in BER), MLH1 (77), MSH2 (77, 78), MSH3 (77, 79) and EXO1 (77, 80) (involved in MMR), XRCC3 (70, 76, 81, 83, 84) and RAD51 (81–84, 90) (involved in HR), Ku70 (85)/80 (86, 87), XRCC4 (88, 89) and Lig4 (83)(involved in HR).