Success of short-term, higher-dose imatinib mesylate to induce clinical response in FIP1L1-PDGFRalpha-negative hypereosinophilic syndrome.

Presence of the oncogenic mutation FIP1L1-PDGFRalpha in hypereosinophilic patients is predictive of hematologic response to imatinib mesylate. However, most patients with hypereosinophilic syndrome (HES) do not have this mutation and have not responded to imatinib doses traditionally successful in patients who test positive for FIP1L1-PDGFRalpha. A patient with FIP1L1-PDGFRalpha-negative HES who had intolerance of interferon alpha-2b and hydroxyurea was treated with escalating doses of imatinib. At 800 mg of imatinib daily, eosinophilia was controlled, allowing prednisone tapering and control of clinical and laboratory-detected abnormalities. HES patients who test negative for FIP1L1-PDGFRalpha may benefit from a trial of higher-dose imatinib.