TET2 mutations are common in both myeloid blood malignancies (acute myeloid leukemia/myelodysplastic syndrome, chronic myelomonocytic leukemia) and T-cell lymphoma, particularly in angioimmunoblastic T-cell lymphoma, which raises questions as to the original cell that underwent the TET2 mutation in NK-LGL leukemia. This evidence concerns the gene TET2 and chronic myelomonocytic leukemia.