[Hypereosinophilic syndromes]

Hypereosinophilic syndromes. Hypereosinophilic syndromes (HES) is a protean condition defined by chronic blood eosinophilia ≥ 1.5 G/L (> 1 month) leading to eosinophilic-related organ damage. HES subtypes includes neoplastic (clonal) disorders (HESN, that comprises FIP1L1-PDGFRA- related chronic eosinophilic leukemia and myeloproliferative and myelodysplastic syndromes associated with eosinophilia) and reactive HES (HESR, that aggregates all conditions e.g. parasitic infections, adverse drug reactions, inflammatory or neoplastic diseases that lead to the production of Th2-related cytokines and thereby to non-clonal hypereosinophilia). HESR also includes the lymphoid variant of HES (HESL), a chronic clonal indolent T-cell lymphoproliferative disorder in which mature peripheral T cells secrete high amounts of IL-5, leading to the polyclonal expansion of eosinophils. Despite an extensive etiological workup, approximately 50% of HES remain of undetermined cause. HES-related clinical manifestations are highly diverse, but dermatological, respiratory and gastro-intestinal symptoms are the most frequent. The long-term prognosis is driven by cardiac involvement and, for patients with HESN and HESL, by the risk of acute transformation into high-grade hematological malignancies. Treatment of HESN relies on tyrosine kinase inhibitors (e.g. imatinib mesylate), while oral glucocorticoids are the usual the fist-line therapy for HESR (including SHEL). In this setting, second-line treatments include hydroxyurea and Peg-interferon alfa-2a. IL-5-targeted therapies are very promising (except for HESN). Yet, to date, their use is restricted to clinical trials and to a compassionate use program dedicated to severe and refractory patients.