Human leucocytic antigen-DR negative acute myeloid leukemia: A diagnostic dilemma for hematopathologist

Background: Acute myeloid leukemia (AML) blast variably express Human leucocytic antigen (HLA).We retrospectively analyzed immunophenotypic and clinical profile of 12 cases of HLA -DR negative AML and correlated with their morphological, cytogenetics and Molecular findings.There is a paucity of literature mentioning morphological, immunophenotypic and cytogenetics characteristics of HLA DR negative AML. Aim: This study was designed to study the morphological, flow cytometric, and cytogenetics characteristics of HLA DR negative AML/non acute Promyelocytic Leukaemia (APML) cases. Materials and Methods: Seventeen such cases were diagnosed over a period of 1 year and 8 months. Peripheral blood and bone marrow aspiration smears were stained by Wright giemsa and examined by three hematopathologist independently. Immunophenotyping was done using multicolour flow cytometry on BD FACS CANTO II using FACS DIVA software.Conventional Karyotyping was done using Wright giemsa staining (using IKAROS software) and florescent in situ hybridization (FISH) was done using dual color dual fusion probe from Vysis promyelocytic leukemia-retinoic acid receptor alpha (PML-RARA) fusion gene probe. Molecular analysis using reverse transcriptase-polymerase chain reaction (RT-PCR) was done using Thermal Cycler of Applied Biosystem and Gel-Doc by Biorad. Results : Of the 12 cases studied ten were classified as French-American-British (FAB) AML-M1. Two case as FAB AML-M2. Morphologically the cells resemble abnormal promyelocytes with bilobation, convoluted and folded nucleus, inconspicuous nucleoli and open chromatin (n = 11) and with blastic morphology, open chromatin, and inconspicuous nucleoli (n = 1).Karyotyping analysis shows normal karyotype (n = 10), del 9q-(n = 1), and t (5:9) (n = 1) respectively.FISH done using dual color dual fusion probe (n = 12) do not show PML-RARA fusion signal.RT-PCR (n = 12) revealed a negative result for PML - RARA fusion transcripts. Conclusion: HLA-DR negativity does not always imply a diagnosis of APML. A Cytogenetic (FISH/conventional karyotype) or molecular (RT-PCR) evidence of t (15:17) or PML-RARA fusion gene transcript is a must to stamp a case as APML. Morphology and Flow cytometric findings are only complementary to Cytogenetic/Molecular findings.