HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: Three HDAC inhibitors have been approved by the US Food and Drug Administration for the treatment of TCL: romidepsin for patients with CTCL who have received ≥1 prior systemic therapy and for patients with PTCL who have received ≥1 prior therapy, vorinostat for cutaneous manifestations in patients with CTCL who have progressive, persistent, or recurrent disease on or following two systemic therapies, and belinostat for patients with relapsed or refractory PTCL [16, 20, 21].