HDAC9 and mature T-cell and NK-cell non-Hodgkin lymphoma: Thus far, HDAC inhibition using Romidepsin showed promising results for the treatment of r/r PTCL [198]; this, however, could not be translated into treatment as a first-line therapy, as combinations of Romidepsin with CHOP were found to be inappropriate for improving progression-free survival of previously untreated PTCL patients [199,200].