TBX21 and mature T-cell and NK-cell non-Hodgkin lymphoma: However, two recent studies report frequencies of DNMT3A mutations in PTCL-NOS categorized as PTCL-NOS-GATA3 or PTCL-NOS-TBX21 [45] as <15% [33, 38], indicating aberrant accumulation of these mutations in Tfh lymphomas.