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CSF3R mutations are uncommon in AML; however, when they occur, they are often associated with core-binding factor gene abnormalities and CEBPAdm. An in-depth understanding of the interaction between these genetic alterations could facilitate a clearer understanding of the role of CSF3R mutations in AML development and may be used for disease classification, prognosis, and the development of targeted therapy.

Fusion genes (FGs) are important genetic abnormalities in acute leukemias, but their variety and occurrence in acute leukemias remain to be systematically described. Whole transcriptome sequencing (WTS) provides a powerful tool for analyzing FGs. Here we report the FG map revealed by WTS in a consecutive cohort of 1000 acute leukemia cases in a single center, including 539 acute myeloid leukemia (AML), 437 acute lymphoblastic leukemia (ALL), and 24 mixed-phenotype acute leukemia (MPAL) patients. Bioinformatic analysis identified 792 high-confidence in-frame fusion events (296 distinct fusions) which were classified into four tiers. Tier A (pathogenic), B (likely pathogenic), and C (uncertain significance) FGs were identified in 61.8% cases of the total cohort (59.7% in AML, 64.5% in ALL, and 63.6% in MPAL). FGs involving protein kinase, transcription factor, and epigenetic genes were detected in 10.7%, 48.5%, and 15.1% cases, respectively. A considerable amount of novel FGs (82 in AML, 88 in B-ALL, 13 in T-ALL, and 9 in MPAL) was identified. This comprehensively described real map of FGs in acute leukemia revealed multiple FGs with clinical relevance that have not been previously recognized. WTS is a valuable tool and should be widely used in the routine diagnostic workup of acute leukemia.

The RARG gene is a member of the nuclear hormone receptor superfamily and shares high homology with RARA and RARB. RARA is involved in translocation with PML in acute promyelocytic leukaemia (APL). Little is known about RARB or RARG rearrangement. RARG fusions were reported in only five APL patients and the partner genes were NUP98, PML and CPSF6. Here, we report NPM1 as a new partner gene of RARG and identify a unique NPM1-RARG-NPM1 chimeric fusion for the first time in an old male with morphological and immunophenotypical features of hypergranular APL but lacking response to all-trans retinoic acid (ATRA) and arsenic trioxide (As 2 O 3 ) therapy. The structural features of the fusion transcript may account for the clinical resistance of the patient. RARG fusion is rare but recurrent in APL, further investigation in larger cohorts is expected to assess frequency, clinical characteristics and outcomes of RARG-translocation in APL.

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