It was reported that HDAC6 inhibition increases the acetylation of p53 in tumor cells, which leads to upregulated expression of genes related to cell cycle control and apoptosis, including p21 cyclin-dependent kinase (CDK) inhibitor, which can be induced with HDAC inhibition in p53-dependent and -independent ways [37,96]. This evidence concerns the gene HDAC9 and neoplasm.