CDKN1A and cancer: Histone deacetylase (HDAC) inhibitors are a group of anticancer agents that modify the post-transcriptional activity of proteins by inactivating histone deacetylase enzymes, thereby leading to cell cycle arrest by increasing cyclin-dependent kinase inhibitor 1 (p21) levels, and cell death or apoptosis of cancer cells by activation of p53 [182,183].