To date, four HDAC inhibitors (panobinostat, romidepsin, heliostat, and vorinostat) have been approved by the United States Food and Drug Administration for the treatment of hematological malignancies, such as cutaneous T-cell lymphoma, peripheral T-cell lymphoma, and multiple myeloma [35–39]. This evidence concerns the gene HDAC9 and peripheral T-cell lymphoma, not otherwise specified.