Cryptic PML-RARα positive acute promyelocytic leukemia with unusual morphology and cytogenetics.

Acute Promyelocytic Leukemia (APL) is different from other forms of acute myeloid leukemia (AML), to the reason being the potential devastating coagulopathy and the sensitivity to all-trans retinoic acid (ATRA) and arsenic trioxide (As 2 O 3 ). We hereby present a case of APL, morphologically distinct from the hypergranular APL; however, the flow cytometry revealed a characteristic phenotype showing dim CD45, bright CD13, bright CD33 and dim CD117 positivity. These were negative for CD34, HLA-DR, B-lymphoid and T-lymphoid lineage markers. Conventional cytogenetics revealed a distinct karyotype of a male with translocation t(4;15)(q34.2:q26.3). However, interphase fluorescence-in-situ hybridization (FISH) revealed PML/RARA fusion signal on chromosome 15 in 90% cells. The cryptic translocations may be missed on conventional cytogenetics, however, need to be picked by other techniques as FISH.