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A 46-year-old previously healthy man presented with a 2-week history of fever and diarrhoea. A full blood count showed: white blood cells 49·5 × 109/l (blast cells 42 × 109/l, eosinophils 1·5 × 109/l), haemoglobin concentration 166 g/l and platelets 52 × 109/l. There was no basophilia and Auer rods were not seen. A coagulation screen was normal. The bone marrow was markedly hypercellular with over 80% cellularity, including 80% myeloblasts, which were positive for CD13, CD33, CD43, CD64 (dim), CD117 and myeloperoxidase, and negative for CD14, CD15, CD34, CD45, CD64, terminal deoxynucleotidyl transferase, human leucocyte antigen (HLA)-DR and lysozyme. Notably, there were 12% eosinophil precursors, many of which displayed large basophilic granules admixed with eosinophilic granules (image), morphologically strongly reminiscent of acute myelocytic leukaemia with inv(16)(p13·1q22) or t(16;16)(p13·1;q22). Fluorescence in situ hybridization was negative for an inversion 16, as well as for PDGFRA and PDGFRB rearrangement. Karyotypic analysis demonstrated a normal male karyotype. Molecular analysis showed a FLT3 internal tandem duplication and an NPM1 exon 12 mutation. This analysis was negative for the FLT3-D835 variant. The patient underwent induction chemotherapy (cytarabine and idarubicin; 7 + 3) with a diagnosis of acute myeloid leukaemia. He achieved complete remission, and was referred for evaluation for bone marrow transplantation. The absence of inversion 16 and other recurrent abnormalities associated with eosinophilia was a surprise in this case given the striking morphological features.