The Efficacy of Imatinib Mesylate in the Treatment of a Rare Lytic Bone Lesion Caused by Hypereosinophilic Syndrome/Chronic Eosinophilic Leukemia.

Case: We report a patient with hypereosinophilia-associated massive osteolytic lesion of the sacrum who was admitted to our hospital. Genetic analysis revealed that atypical eosinophilic cells were positive for FIP1-like-1-platelet-derived growth factor receptor-alpha (FIP1L1-PDGFRA) fusion gene. Treatment was initiated with oral administration of imatinib mesylate. The patient responded rapidly to this medication with a marked reduction in eosinophilia both from the peripheral blood and FIP1L1-PDGFRA fusion gene in the bone marrow within 2 weeks, followed by gradual osteosclerotic repair of the sacrum. Conclusions: This case study found that the drug imatinib proved very effective in the treatment of this rare condition. [ABSTRACT FROM AUTHOR]