Bone marrow neoplastic

Bone marrow - neoplastic myeloid

Myeloproliferative neoplasms (MPN)

Chronic eosinophilic leukemia

Editorial Board Member: Genevieve M. Crane, M.D., Ph.D.
Deputy Editor-in-Chief: Debra L. Zynger, M.D.
Lynh Nguyen, M.D.
Ling Zhang, M.D.

Last author update: 1 January 2018
Last staff update: 12 January 2023 (update in progress)

Copyright: 2002-2023,, Inc.

PubMed Search: Chronic eosinophilic leukemia[TI] full text[sb]

Lynh Nguyen, M.D.
Ling Zhang, M.D.
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Cite this page: Nguyen L, Zhang L. Chronic eosinophilic leukemia. website. Accessed June 4th, 2023.
Definition / general
  • Chronic eosinophilic leukemia, not otherwise specified (NOS)
  • Persistent increase in eosinophils in peripheral blood (≥ 1.5 x 109/L), bone marrow and tissue
  • May be accompanied by increased blasts (< 20%) or clonal cytogenetic or molecular genetic abnormalities (Am J Hematol 2017;92:1243)
  • Organ damage may occur as a result of infiltration and release of eosinophilic granules that contain cytokines and humoral factors
  • Other clonal myeloid neoplasms and reactive eosinophilia should be excluded
  • In the absence of blasts or evidence to prove clonality, a diagnosis of idiopathic hypereosinophilic syndrome should be made
Essential features
  • Rare myeloproliferative neoplasm characterized by a gradual increase in circulating eosinophils with cytologic atypia (rarely may be absent), left shifted granulocytic maturation and often hepatomegaly or splenomegaly
  • Organ / tissue infiltration by eosinophils and eosinophilic microabcesses are frequently present, leading to tissue damage and organ dysfunction
  • Clinical course is variable, transformation to acute myeloid leukemia is common and prognosis is generally poor
    • Fatal cardiac damage has been documented secondary to the release of cytokines produced by eosinophils
    • This diagnosis should be made after exclusion of reactive causes of eosinophilia, myeloid and lymphoid neoplasms associated with PDGFRA, PDGFRB, FGFR1 rearrangements and JAK2 fusion, and confirmation of clonality (Am J Hematol 2017;92:1243), see full WHO criteria below
Cell of origin
  • Pluripotent hematopoietc stem cell, in some cases a pluripotent lymphoid-myeloid stem cell
  • Due to difficulty in distinguishing chronic eosinophilic leukemia, not otherwise specified from idiopathic hypereosinophilic syndrome, the true incidence is unknown
  • Some reports show predilection for men in the seventh decade (Mod Pathol 2016;29:854, Am J Hematol 2012;87:643)
  • Peripheral blood and bone marrow are always involved
  • Splenic and hepatic involvement are also common
  • Other frequent sites of involvement include the heart, lungs, central nervous system, skin and gastrointestinal tract
Clinical and laboratory features
  • In some cases patients may be asymptomatic, longstanding eosinophilia without specific etiology (i.e. no allergy, asthma, drug reaction, parasitic infection or connective disease)
    • Eosinophil count can vary from 1.5 - 400 x 109/L
  • Can have leukocytosis (20 - 30 x 109/L), anemia, thrombocytopenia or thrombocytosis
  • Symptoms: weight loss, night sweats, fever (12%), fatigue (26%), myalgias or angioedema (14%), cough (12%), dyspnea (16%), pruritus and diarrhea
  • Skin manifestations are the most common, followed by lung (44%) and GI tract (38%)
  • Cardiovascular
    • Endomyocardial fibrosis followed by restrictive cardiomegaly
    • Hypertension, atherosclerosis and heart failure
    • Scarring of mitral and tricuspid valves leading to regurgitation, thrombi formation and embolization in end organs
  • Peripheral neuropathy, CNS dysfunction and rheumatologic findings (Am J Hematol 2012;87:643)
  • Natural history varies considerably between individuals
Diagnostic criteria (WHO 2017 classification)
  • Persistent eosinophilia (≥ 1.5 x 109/L) in which reactive causes have been excluded
  • Does not meet diagnostic criteria for chronic myeloid leukemia with t(9;22)(q34.1;q11.2) / BCR-ABL1 gene fusion, polycythemia vera, essential thrombocythemia, primary myelofibrosis, chronic neutrophilic leukemia, chronic myelomonocytic leukemia, atypical chronic myeloid leukemia (BCR-ABL1 gene fusion negative) or systemic mastocytosis
  • Blasts < 20% of peripheral blood and bone marrow cells and does not have the following cytogenetic aberrations:
    • PDGFRA, PDGFRB or FGFR1 rearrangements
    • t(8;9)(p22;p24.1) / PCM1-JAK2, t(9;12)(p24.1;p13.2) / ETV6-JAK2 or t(9;22)(p24.1;q11.2) / BCR-JAK2 fusions
    • inv(16)(p13.1;q22) or t(16;16)(p13.1;q22) / CBFB / MYH11, t(15;17)(q22;q11-12) / PML-RARA or t(8;21)(q22;q22.1) / RUNX1 / RUNX1T1
    • t(9;22)(q24;q31) / BCR-ABL1 fusions
  • Presence of clonal cytogenetic or molecular genetic abnormality(ies)* or a blast count ≥ 2% in the peripheral blood or ≥ 5% in the bone marrow
    • *Certain gene mutations (e.g. DNMT3A, TET2, ASXL1 with variant allele frequency ≥ 2%) can be seen in a subpopulation of elderly patients who do not have hematologic disorders, otherwise known as clonal hematopoiesis of indeterminate potential
Prognosis and predictive factors (2017 WHO classification)
Case reports
  • 52 year old man with t(5;12)(q31;p13) / ETV6-ACSL6 gene fusion, a novel variant of myeloid proliferative neoplasm with eosinophilia (Hum Pathol (N Y) 2016;5:6)
  • 68 year old woman with liver infiltration resembling Budd-Chiari syndrome (Rinsho Ketsueki 2007;48:505)
  • 72 year old man with autoimmune hemolytic anemia and erythrophagocytosis by eosinophils (Am J Hematol 2006;81:458)
Microscopic (histologic) description
  • Peripheral blood:
    • Striking eosinophilia (≥ 1.5 x 109/L) mainly composed of mature eosinophils and occasional immature eosinophilic precursors
      • Circulating blasts can be seen but comprise < 20%
    • Spectrum of nonspecific eosinophil abnormalities: sparse granulation, cytoplasmic vacuolation, nuclear hyper / hyposegmentation or increased size
    • Occasional cases show normal eosinophilic morphology and lack dysplasia; however, lack of dysplasia favors reactive eosinophilia (Mod Pathol 2016;29:854)
    • Often accompanied by neutrophilia, some with mild monocytosis (> 1 x 109/L) and a few with mild basophilia
  • Bone marrow:
    • Hypercellular due to eosinophilic proliferation; however, maturation is orderly without disproportionate increase in myeloblasts
    • Charcot-Leyden crystals often present
    • Usually normal erythropoeisis and megakaryocytopoiesis, however, abnormal megakaryocytes are occasionally seen
    • Increased myeloblasts (commonly 5 - 19% in bone marrow)
    • 1/3 of cases show myelofibrosis; severe fibrosis is rare
  • Tissue:
    • Eosinophilic infiltration or microabcesses
    • Charcot-Leyden crystals
    • Fibrosis (caused by the degranulation and release of eosinophilic basic and cationic proteins)
Microscopic (histologic) images

Contributed by Lynh Nguyen, M.D. and AFIP images

Numerous eosinophilic precursors

Myeloid preponderance

Marked hypercellularity

Granulocytic hyperplasia

Reticulin fibrosis

Markedly fibrotic marrow

Markedly hypercellular

Peripheral smear images

Contributed by Lynh Nguyen, M.D.

Moderately degranulated eosinophils

Patient with longstanding hypereosinophilia

Circulating abnormal eosinophils

Marked increased eosinophils

  • No specific immunophenotype has been associated with chronic eosinophilic leukemia, not otherwise specified; however, immunophenotyping is important to exclude T lymphocyte driven eosinophilia or acute leukemia
Electron microscopy images

AFIP images

Abnormal eosinophil with decreased granules

Molecular / cytogenetics description
Differential diagnosis
Board review style question #1
Which of the following is useful in definitively diagnosing the lymphocytic variant of hypereosinophilic syndrome?

  1. Abnormal T cell population, e.g. CD3- / CD4+
  2. Elevated IL5 level
  3. Eosinophilia ≥ 1.5 k/L
  4. Eosinophilic tissue infiltrate
  5. Skin rush and pruritus
Board review style answer #1
A. Abnormal T cell population, e.g. CD3- / CD4+. Lymphocytic variant of hypereosinophilic syndrome is characterized by abnormal cytokine release by clonal T cells. CD3- / CD4+ T cells are often found in circulating blood but CD3+ / CD4+ / CD7- and CD3+ / CD4- / CD8- T cells have also been described. TCRγδ rearrangements are frequently identified in these patients; however, TCRαβ+ L-HES has also been reported. Elevated IL5 levels, eosinophilia and eosinophilic infiltration can be seen in a number of reactive, neoplastic and iatrogenic conditions and are not diagnostic or specific for L-HES. Pruritus and skin rash can occur as a result of eosinophilia but this finding is not specific.

Comment Here

Reference: Chronic eosinophilic leukemia, not otherwise specified (CEL, NOS)
Board review style question #2
Which of following morphologic or molecular genetic findings is frequently identified in chronic eosinophilic leukemia, not otherwise specified?

  1. Dysplastic noneosinophilic granulocytes
  2. ETV6-JAK2 fusion
  3. Hypercellular marrow with increased eosinophils
  4. KIT D816V gene mutation
  5. Marked monocytosis
Board review style answer #2
C. Hypercellular marrow along with eosinophilic proliferation, though nonspecific, is the most common feature for CEL-NOS.

Comment Here

Reference: Chronic eosinophilic leukemia, not otherwise specified (CEL, NOS)
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