Chronic eosinophilic leukemia (CEL) is a chronic myeloproliferative disorder of unknown etiology in which a clonal proliferation of eosinophilic precursors results in persistently increased numbers of eosinophils in the blood, bone marrow, and peripheral tissues. In CEL, the eosinophil count is greater than or equal to 1.5 × 109 /L in the blood. To make a diagnosis of CEL, there should be evidence for clonality of the eosinophils or an increase in blasts in the blood or bone marrow. In many cases, however, it is impossible to prove clonality of the eosinophils, in which case, if there is no increase in blast cells, the diagnosis of idiopathic hypereosinophilic syndrome (HES) is preferred. Because of the difficulty in distinguishing CEL from HES, the true incidence of these diseases is unknown, though they are rare. In about 10% of patients, eosinophilia is detected incidentally. In others, the constitutional symptoms found include:[1,2]
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No single or specific cytogenetic or molecular genetic abnormality has been identified in CEL.
(Refer to the PDQ summaries on Fever, Sweats, and Hot Flashes; Fatigue; Cardiopulmonary Syndromes; Pain; Pruritus; and Gastrointestinal Complications for information on many of the symptoms listed above.)
The optimal treatment of CEL remains uncertain, partially on account of the rare incidence of this chronic myeloproliferative disorder and the variable clinical course, which can range from cases with decades of stable disease to cases with rapid progression to acute leukemia. Case reports suggest that treatment options include bone marrow transplantation and interferon-alpha.[3,4]
Case reports suggest symptomatic responses to imatinib mesylate for patients with HES who have not responded to conventional options.[6,7,8][Level of evidence: 3iiiDiv] Imatinib mesylate acts as an inhibitor of a novel fusion tyrosine kinase, FIP1L1-PDGFR alpha fusion tyrosine kinase, which results as a consequence of interstitial chromosomal deletion.[6,9][Level of evidence: 3iiiDiv] HES with the FIP1L1-PDGFR alpha fusion tyrosine kinase translocation has been shown to respond to low-dose imatinib mesylate.