Comparing the regulation of CDKN1A with the results from cell cycle analysis revealed that Cal33, Detroit 562, UD-SCC-2, and UM-SCC-47 showed G0/G1 arrest in the combined treatment compared to IR corresponding with an increased expression of CDKN1A. Foy et al. also showed that an elevated p21 level in tumor cells correlates with G1 arrest45. The gene discussed is CDKN1A; the disease is neoplasm.