Acute promyelocytic leukemia with normal karyotype initially diagnosed on bone marrow touch imprints

which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. A 26-year-old man visited our hospital for the evaluation of leukopenia, an incidental finding during a routine health examination. His complete blood count values were as follows: leukocytes, 1.09×10 dry tap with unremarkable finding. On touch imprints, however, abnormal promyelocytes with multiple Auer rods, termed " faggot cells " , were observed in several fields (A, B; Wright staining, ×1,000), suggesting acute promyelocytic leukemia (APL). BM biopsy was hypercellular with diffuse infiltration of leukemic cells positive for myeloperoxidase. However, cytogenetic testing showed normal karyotype without t(15;17). Subsequently, reverse transcription-PCR using a re-aspirated specimen was performed, revealing the presence of the PML/RARA fusion transcript. No chromosomal abnormalities were found on cytogenetic examination of the re-aspirate specimen. Cases of APL lacking t(15;17) with complex variant rearrangements or submicroscopic insertion have been reported. The latter is considered as cryptic or masked t(15;17), occurring in approximately 5% of cases. The importance of adequate preparation and careful examination of BM touch imprints has been well described in the literature but may be overlooked at times.