HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: The natural cyclodepsipeptide, romidepsin 11 (Fig. 7), was approved for CTCL and PTCL.76,77 It is considered a broad spectrum HDAC inhibitor, acting mainly on class I HDAC and at relatively higher concentrations on class II HDAC.78 In 2024, data of a phase 1b/2a trial revealed the significance of a combination of a phosphoinositide-3-kinase inhibitor such as duvelisib and a HDAC inhibitor such as romidepsin in T-cell lymphoma.79