[1226] Immunophenotypic Pattern of Eosinophilia by Flow Cytometry.

Donghong Cai, Yusong Yang, Wojciech Gorczyca. SUNY Downstate Medical Center; Supported by CAP Foundation, Brooklyn, NY; Genzyme Genetics, New York, NY

Background: Eosinophilia (EO) is seen in variety of reactive conditions and certain neoplasms. In the latter, EO may present as a benign component or represent myeloproliferative neoplasm (MPN) with clonal eosinophilic expansion. MPN categories with EO include chronic eosinophilic leukemia (CEL) and MPN with rearrangement of PDGFRA, PDGFRB or FGFR1. Identification of EO by flow cytometry (FC) may be difficult due to (1) lack of eosinophil-specific markers, (2) overlap of phenotypic features of eosinophils with other populations and (3) low forward scatter leading to confusion with cellular debris. Based on immunophenotypic analysis of 14 cases, we present easily recognizable FC pattern of EO.
Design: Twelve cases of EO diagnosed by FC and morphology were included in this study. All patients represented de novo diagnosed EO without prior history of acute leukemia or lymphoproliferative disorder. We used 6-color FC with following markers: CD2, CD3, CD4, CD5, CD7, CD8, CD10, CD11b, CD11c, CD13, CD14, CD16, CD19, CD20, CD33, CD34, CD38, CD45, CD56, CD64, CD117, HLA-DR, forward FSC) and side (SSC) scatter. The FC pattern of EO was compared with that of benign granulocytes, basophils and monocytes, MDS, acute promyelocytic leukemia (APL) and CML.
Results: The age ranged from 19 to 87 (average: 58.5). The percent of eosinophils varied from 12 to 75 (average: 39%). All cases were characterized by high SSC, very low FSC, bright CD45 and positive CD11b, CD11c, CD13 and CD33. Eosinophils were negative for CD10, CD16, CD56, HLA-DR, B- and pan-T antigens, CD34, CD117, CD14 and CD64. One case with confirmed FIP1L1-PDGFRA translocation displayed aberrant CD4. Neutrophils differed from EO by positive CD10 and CD16, higher FSC and brighter expression of CD13, CD33, CD11b and CD11c. APL differed by high FSC, brighter CD33, positive CD64 and CD117 and lack of CD11b/CD11c. Basophils were characterized by low SSC, dimmer CD45, brighter CD38 and higher FSC. Dysplastic granulocytes (MDS patients), were often negative for CD10 and/or CD16, differed from EO by dimmer CD45, decreased SSC, higher FSC and/or positive CD56. Monocytes differed by positive CD2, CD4, CD14, CD64 and HLA-DR, and lower SSC.
Conclusions: Although there is no specific antigenic marker for eosinophils, combination of very low FSC with phenotypic pattern and cytology allows for easy recognition of EO by FC, their differentiation from other benign or malignant hematopoietic populations and prompt additional testing for further characterization and final subclassification.
Category: Hematopathology

Tuesday, March 1, 2011 1:00 PM

Poster Session IV # 171, Tuesday Afternoon


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