Several HDAC inhibitors have been demonstrated therapeutic efficacy by clinical trials, including vorinostat (SAHA) in cutaneous T‐cell lymphoma (CTCL) [14], panobinostat in multiple myeloma [15], romidepsin in peripheral T‐cell lymphoma (PTCL) [16], and chidamide in PTCL, breast cancer and colorectal cancer [17, 18, 19]. The gene discussed is HDAC9; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.