Maintenance therapy with imatinib appears necessary despite molecular remission in FIP1L1-PDGFRA fusion gene positive hypereosinophilic disorder.

Patients with primary hypereosinophilic disorders who are positive for the FIP1L1-PDGFRA fusion gene mutation are highly responsive to therapy with imatinib mesylate. A 35-year-old man with FIP1L1-PDGFRA positive hypereosinophilic syndrome and cardiac involvement, was treated with imatinib 100 mg daily. Hematologic and molecular remission and reversal of end-organ damage was achieved. He was then lost to follow up for 19 months. Imatinib successfully reinduced hematologic and molecular remission but worsening cardiac involvement was not reversed. Our experience and a review of limited literature suggest that imatinib maintenance therapy is necessary despite molecular remission of the FIP1L1-PDGFRA mutation.