HDAC9 and primary cutaneous T-cell non-Hodgkin lymphoma: Although the function of individual HDAC isoforms is not fully understood in cell and cancer biology, several pan-selective HDAC inhibitors, such as SAHA (Vorinostat), Belinostat, Panobinostat, Chidamide and Romidepsin (FK228), have been approved for the treatment of cutaneous T-cell lymphoma [2,3,4].