HLA-DR positive acute promyelocytic leukaemia (APML) with cryptic PML::RARA fusion

We report the case of a 42-year-old female presented with cytopenia and abnormal promyelocytes on blood film. The promyelocytes were HLA-DR positive by flow cytometry. The rapid FISH for PML::RARA was negative. Myeloid NGS identified PML::RARA fusion, which was confirmed by molecular karyotyping and PCR. She was treated with ATRA and ATO to complete molecular remission. This case highlighted the importance of using rapid RNA sequencing to identify cryptic fusion and rare fusions and combining morphologic, immunophenotypic, cytogenetic and molecular analyses to ensure correct diagnosis and optimal management.