CDKN1A and neoplasm: As HDACi treatment commonly leads to prominent upregulation of the cyclin-dependent kinase inhibitor p21cip1/waf1 (p21) via p53-dependent or -independent induction of cyclin-dependent kinase inhibitor 1A (CDKN1A) and associated G1 or G2 arrest in cells, combined effects of HDACi and TRAIL sensitize tumor cells to overcome TRAIL resistance [130,134,135,136].