CDKN1A and cancer: However, overexpression of p21Cip1 (cyclin-dependent kinase inhibitor 1), p27Kip1 (cyclin-dependent kinase inhibitor 1B), p14ARF (ARF tumor suppressor), and p16INK4A (cyclin-dependent kinase inhibitor 2A) cell cycle inhibitors was observed to not only inhibit proliferation but be sufficient for inducing differentiation in some cancer cells (Adachi et al., 1997; Kranenburg et al., 1995; Matushansky et al., 2000).