BACKGROUND: Hypereosinophilic syndromes (HESs) are chronic disorders that require
long-term therapy to suppress eosinophilia and clinical manifestations. Corticosteroids are
usually effective, yet many patients become corticosteroid refractory or develop
corticosteroid toxicity. Mepolizumab, a humanized monoclonal anti-IL-5 antibody, showed
corticosteroid-sparing effects in a double-blind, placebo-controlled study of FIP1L1/PDGFRA-
negative, corticosteroid-responsive subjects with HESs. OBJECTIVE: We evaluated long …