Being that senescence is the primary mechanism of radiation-induced cell death in HNSCC cells,30 a senescence-associated β-galactosidase (SA-β-gal) staining was performed and showed that 4 days after treatment with 4-Gy ionizing radiation, cells with wtp53 had a significantly higher SA-β-gal-positive staining (48–60%) compared with the SA-β-gal-positive staining in TP53 null and all TP53 mutant cells (less than 5% Figures 1b and c). Here, TP53 is linked to head and neck squamous cell carcinoma.