We further show that pre-treatment with both MK-8776 and MK-1775 results in a marked decrease in the percentage of cells with high numbers of RAD51 foci at both 8 and 24 h post-irradiation in all three HNSCC cell lines, indicating a reduction in the repair efficiency of DSBs through HR. This evidence concerns the gene RAD51 and head and neck squamous cell carcinoma.