Together, our selective radiosensitizing effect of CHK1 inhibition of radioresistant HNSCC cells (Figure 5) and the observation that most proteins informative of HNSCC patient survival were directly or indirectly associated with replication (Figure 3), suggest that inhibitors to generally inactivate the S-phase DNA damage response, such as CHK1 or ATR [16], are promising options for future advancement of existing therapies. This evidence concerns the gene CHEK1 and head and neck squamous cell carcinoma.