CDKN1B and cancer: Activation of p38α results in downstream activation of a key anti-cancer checkpoint, p53 [42], together with a number of regulators of cell cycle entry, including the cyclin-dependent kinase inhibitors, p16 (CDKN2A/p16Ink4a), p21 (CDKN1A/Waf1) and p27 (CDK1B/p27Kip1) [43].