HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: Romidepsin (Istodax), a histone deacetylase (HDAC) inhibitor, was approved by the US Food and Drug Administration (FDA) in November 2009 for the treatment of cutaneous T-cell lymphoma (CTCL) in patients who have received at least one prior systemic therapy and in May 2011 for the treatment of PTCL in patients who have received at least one prior therapy (Celgene Corporation, 2014).