Chronic eosinophilia is habitually associated with allergic, infectious, inflammatory, neoplastic and endocrine conditions and exposure to certain drugs and toxic agents. However, eosinophilic proliferation may be primary, without identifiable causes, or provoked by clonal hematopoietic stem cell proliferation. Gene fusions involving PDGFR-α, PDGFR-β, and FGFR1 predispose patients to rare conditions with chronic myeloproliferation or lymphoproliferation, alterations in peripheral blood and bone marrow and diffuse tissue injury due to the release of cytokines and humoral factors from eosinophilic granules. The presence of the PDGFR-α rearrangement is commonly related to chronic eosinophilic leukemia, with alterations in peripheral mastocytes and neutrophils, and rarely to acute myeloid leukemia or T lymphoblastic lymphoma with eosinophilia. The most prevalent PDGFR-α rearrangement is one resulting from an interstitial deletion in the long arm of chromosome 4, that allows the formation of a neogene from the fusion of the FIP1L1 and PDGFRα genes. This codes a constitutively active tyrosine kinase, which can be inhibited by imatinib mesylate. In 2002, the successful treatment of a patient using imatinib to treat hypereosinophilic syndrome was reported. Since then, this drug has been utilized with fast, complete and lasting clinical responses. Here we describe a case of chronic eosinophilic syndrome with expression of the FIP1L1-PDGFR-α rearrangement.
Eosinophilia; gene rearrangement; in situ hybridization, fluorescence; hypereosinophilic syndrome; leukemia
