PMC9879720_01
A. Morphology, Karyotyping and FISH analysis of bone marrow smear at first consultation. (A) Several promyelocytes were shown in the bone marrow aspirate (a, b) and peripheral blood smear (c, d), (A) Wright-Giemsa staining, x 100, (B-D) Wright-Giemsa staining, x 1000. (B) Karyotype of the aberrant clone showing t(12;19)(q13;q13.1). (C) Fluorescence in situ hybridization using PML::RARA dual-color, dual-fusion translocation probes and corresponding metaphase chromosomes of the same cell. There was failed to detect the PML::RARA transcript.
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Bone marrow aspirates presented markedly myeloproliferative hyperactivity with 80% hypergranular promyelocytes ( Figure 1A a  and  b ), and peripheral blood smear showed POX strong positive with 65% hypergranular promyelocytes ( Figure 1A c  and  d ). However, the cytogenetic analysis showed the karyotype of 46, XY, t(12;19)(q13;q13.1), different from the typical reciprocal chromosomal translocation t(15;17)(q24;q21) ( Figure 1B ). And both multiplex polymerase-chain-reaction (PCR) and fluorescence in situ hybridization (FISH) failed to detect the typical PML-RARA transcript in the BM sample ( Figure 1C ).
(A). Electrophoresis of reverse transcription-polymerase chain reaction (RT-PCR) products from the patient showed distinct HNRNPC::RARG and RARG::HNRNPC fusion transcripts. (B). Sanger sequencing showing the junction of the HNRNPC::RARG and RARG::HNRNPCP fusion transcripts respectively. (C). The structures of HNRNPC and RARG gene rearrangements and the construction of the corresponding chimeric proteins. (D). Schematic representation of the HNRNPC::RARG and RARG::HNRNPC fusion proteins and its wild-type counterparts. The HNRNPC 3'-region, which contains a cluster of phosphorylation sites, was fused to the RARG 5'-region, which encodes the ligand-binding domain. The HNRNPC 5'-region encodes an RNA recognition motif (RRM), and the segment from RARG encodes a DNA binding domain (DBD).
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Then we performed a BM aspiration again, which revealed hypercellularity with 50% promyelocytes ( Figure 2 ). Thus, the patient received a second induction chemotherapy of Idarubicin, Cytarabine combined with Venetoclax and finally achieved a complete remission in this therapy ( Figure 2 ).
The novel HNRNPC::RARG fusion APLL patient was salvaged by venetoclax combined IA. (A) Timeline of induction therapies. (B) Bone marrow blast percentages for the patient induction therapy. IA, Idarubicin and Cytarabine; VEN, venetoclax.
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For validation of this gene fusion, we performed RT-PCR and Sanger sequencing to confirm the HNRNPC::RARG fusion transcript in this patient ( Figures 3A, B ). In HNRNPC::RARG, HNRNPC exon 3 was fused in-frame to RARG exon4, and in RARG::HNRNPC, RARG exon 9 was fused in-frame to HNRNPC exon4 ( Figure 3C ). The main domains of RARG and HNRNPC were preserved on HNRNPC::RARG fusion protein ( Figure 3D ).