Distinct Mutational Pattern of T-cell Large Granular Lymphocyte Leukemia Combined with Pure Red Cell Aplasia: Low Mutational Burden of STAT3

T-cell large granular lymphocyte leukemia (T-LGL) is often accompanied by pure red cell aplasia (PRCA). A high depth of next generation sequencing (NGS) was used for detection of the mutational profiles in T-LGL alone (n = 25) and T-LGL combined with PRCA (n = 16). Beside STAT3 mutation (41.5%), the frequently mutated genes included KMT2D (17.1%), TERT (12.2%), SUZ12 (9.8%), BCOR (7.3%), DNMT3A (7.3%), and RUNX1 (7.3%). Mutations of the TERT promoter showed a good response to treatment. 3 of 41 (7.3%) T-LGL patients with diverse gene mutations were revealed as T-LGL combined with myelodysplastic syndrome (MDS) after review of bone marrow slide. T-LGL combined with PRCA showed unique features (low VAF level of STAT3 mutation, low lymphocyte count, old age). Low ANC was detected in a STAT3 mutant with a low level of VAF, suggesting that even the low mutational burden of STAT3 is sufficient for reduction of ANC. In retrospective analysis of 591 patients without T-LGL, one MDS patient with STAT3 mutation was revealed to have subclinical T-LGL. T-LGL combined with PRCA may be classified as unique subtype of T-LGL. High depth NGS can enable sensitive detection of concomitant MDS in T-LGL. Mutation of the TERT promoter may indicate good response to treatment of T-LGL, thus, its addition to an NGS panel may be recommended.