RRBP1 and hypereosinophilic syndrome: Glucocorticoids are a first-line treatment for idiopathic and FIP1L1-PDGFRA fusion gene-negative HES, while imatinib is the preferred treatment for FIP1L1-PDGFRA-positive HES.[9] Second-line treatments for idiopathic HES include hydroxyurea, interferon-α, imatinib, and mepolizumab.[10] Hormonal therapy serves to interfere with the transcription of proinflammatory cytokines that are essential for the maturation, proliferation, migration, and chemical induction of eosinophils.