In clonal eosinophilia, although corticosteroids generally do not normalize absolute eosinophil counts, they may reduce eosinophil activation and lower their cytotoxic potential pending a precise molecular diagnosis and onset of a specific treatment (as detailed in “Management of FIP1L1::PDGFRA–positive chronic eosinophilic leukemia” and “Management of non-F/P-associated clonal HES” Sections). This evidence concerns the gene FIP1L1 and hypereosinophilic syndrome.