For patients with myeloproliferative HES (M-HES) who test positive for a Fip1-like 1 (FIP1L1)/platelet-derived growth factor receptor alpha (PDGFRA) rearrangement, the tyrosine kinase inhibitor imatinib should be initiated as first-line therapy (3, 5). This evidence concerns the gene PDGFRA and hypereosinophilic syndrome.