Mutations of enzymes regulating DNA methylation: Ten-Eleven Translocation-2 (TET2), DNA methyltransferase-3A (DNMT3A) and isocitrate dehydrogenase-2 (IDH2) are frequently perturbed in angioimmunoblastic T-cell lymphoma (AITL) and PTCL of T-follicular helper phenotype (hereafter referred to in aggregate as T-cell lymphomas of T-follicular helper origin [tTFH]) [3–7]. The gene discussed is TET2; the disease is angioimmunoblastic T-cell lymphoma.