CDKN1A and neoplasm: Senescent cells have a large flattened morphology, stop DNA replication, show increased levels of proteins involved in cell cycle arrest and tumor suppression (such as the tumor suppressor p53 and cyclin-dependent kinase inhibitors [CDKi] p16INK4A, p21CIP1/WAF1, and p15INK4B), and are positive for the senescence-associated β-galactosidase (SA β-gal).