A novel NPM1-RARG-NPM1 chimeric fusion in acute myeloid leukaemia resembling acute promyelocytic leukaemia but resistant to all-trans retinoic acid and arsenic trioxide.

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 (As2O3) 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.