We and others have previously reported that TET2 and DNMT3A mutations were found in apparently normal blood cells, including bone marrow mononuclear cells, and in immature progenitors and blood cells of various lineages isolated from peripheral blood of a few PTCL patients.7, 9, 15, 16, 17 We examined the distribution of TET2, IDH2 and DNMT3A mutations in PD1+ and CD20+ cells. The gene discussed is DNMT3A; the disease is mature T-cell and NK-cell non-Hodgkin lymphoma.