In vitro, belinostat exhibits pan-HDAC inhibition (i.e., classes I, II, and IV HDAC inhibition) and potent growth inhibitory and proapoptotic activities in a variety of tumor cells, including PTCL cells, at nanomolar concentrations (Marks et al., 2000; Poole, 2014; O’Connor, 2015; Steele et al., 2008). This evidence concerns the gene HDAC9 and neoplasm.