CHEK1 and head and neck squamous cell carcinoma: Here, accumulating evidence has shown that targeting enzymes including poly (ADP-ribose) polymerase, ataxia telangiectasia and Rad-3 related, DNA-dependent protein kinase catalytic subunit, and checkpoint kinase 1 can radiosensitise HNSCC cells which should be taken forward in further preclinical studies, with the goal of optimizing the future effective RT treatment of HNSCC.