HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: In recent years, first-line regimens built on a CHOP-like backbone have been studied, but none, including the one combining the histone deacetylase (HDAC) inhibitor romidepsin with CHOP (Ro-CHOP), significantly improved the survival of patients affected by PTCL [41], thus supporting the concept that identifying better treatments remains a major unmet need.