HDAC9 and cancer: Like DNMT inhibitors, small molecules targeting HDAC activity are able to induce positive and negative immunomodulatory effects; in fact, they can increase cancer immunogenicity through the expression of HLA class I genes and tumor antigens and/or block T cell response by the upregulation of ligand for checkpoint inhibitor receptors as well as by reducing the number of Tregs (Setiadi et al., 2007; Shen et al., 2012; Woods et al., 2015).