PB1991 HARLEQUIN CELL: UBIQUITOUS OR PATHOGNOMIC???
Authors: Jain G. , Kumar C. , Chopra A. 
Published: June 2019

Background:Harlequin cells, often called hybrid eosinophilic basophilic precursor are cells harbouring both eosinophilic and basophilic granules in their cytoplasm. Studies have associated these cells with clonal myeloid disorders like acute myeloid leukaemia (AML) with the recurrent cytogenetic abnormality involving CBFB‐MYH11, inv(16)(p13.1q22) or t(16;16)(q13.1;q22) and chronic myelogenous leukaemia (CML) (1,2). However in our experience as a tertiary care centre we found these cells to be ubiquitously present among many bone marrow aspirates without any clonal myeloid neoplasm.Aims:To analyse the prevalence of harlequin cells in various bone marrow aspirates with the aim to establish the diagnostic relevance of these cells, if any.Methods:All the bone marrow aspirates (BMA) and touch preparations (BMTP) submitted for evaluation between the period 1st September 2018 to 30th September 2018 at Laboratory Oncology Unit, All India Institute of Medical Sciences, New Delhi were evaluated. A total of 317 Bone marrow samples were received during this period.Jenner‐ Giemsa stained slides of aspirate and touch preparations were studied with respect to cellularity, M: E ratio, primary diagnosis suspected, presence of Harlequin and any additional observation noted such as hematogones or hemophagocytosis. These parameters were tabulated and the data was analysed.Results:Out of the total 317 aspirates and touch preparations, 63.4 % (201/317) cases showed presence of HQ cells. Eighty three bone marrow aspirates sent for staging evaluation of metastasis, NHL, Hodgkins lymphoma and pancytopenia revealed cellular reactive marrows. All of these also showed HQ cells. A total of 223 BMA which were involved by hemato‐lymphoid neoplasms also showed the presence of HQ cell. Spectrum included new cases of ALL, AML, Multiple Myeloma, POEMS, MDS/MPN, CML, JMML and NHL as well as relapsed cases of AML, ALL and progressive disease in multiple myeloma. Few cases with presence of hematogones [2/201] and erythroid hyperplasia [1/201]also showed these cells.HQ cells were absent in 36.6 % (116/317) cases. 28.4 % (33/116) aspirates were grossly diluted and no opinion was possible thereby explaining the possible absence. 49.4% (41 / 83) of the undiluted bone marrow aspirates had near total replacement or infiltration by > 80 % blasts/plasma cells/ abnormal lymphoid cells. Marked reduction of normal hematopoietic cells in these BMA could be a possible causative factor for absence of HQ cell.Hemophagocytosis was seen in partially diluted aspirates of 6 cases and only one of such case showed the presence of HQ cell. A single diluted BMA also showed the presence of HQ cell.Summary/Conclusion:We would like to conclude that HQ cells can be seen in normal cellular bone marrow aspirates as well as bone marrow aspirates involved by infectious, nutritional, and metastatic and all types of hematolymphoid neoplasms. In contrast to previous reported studies, the presence of this cell does not signify either a myeloid neoplasm [1] nor is it only seen in cases of CML and AML with inv(16) or t(16;16).Presence of HQ cells is thus neither an indicator nor is it pathognomic of any particular hematolymphoid neoplasm.