CDKN2A and neoplasm: For instance, the cyclin-dependent kinase inhibitors (CDKs), CDKN1A (p21Cip1), CDKN1B (p27Kip1), and CDKN2A (p16Ink4A), reprimo (RPRM), stratifin (SFN), and CDK1 are all frequently hypermethylated and play various roles in tumor radioresistance (140).