LIG4 and head and neck squamous cell carcinoma: Given the roles of these key DNA repair enzymes in resolution of IR-induced DNA damage, the potent radiosensitizing effects of either the DNA-PK inhibitor or PARP inhibitor in HNSCC is previously reported (Nowsheen et al., 2011b; Forster et al., 2012; Weaver et al., 2015; Kwon et al., 2016; Fok et al., 2019; Lee et al., 2019; Hernandez et al., 2020).