Imatinib for the treatment of hypereosinophilic syndromes

Hypereosinophilic syndromes (HES) encompass a group of disorders defined by sustained peripheral blood hypereosinophilia >1500/mm³ and evidence of eosinophilia-associated organ impairment. Approximately 10% of HES patients may harbor a cryptic deletion on chromosome 4 leading to formation of the FIP1L1-PDGFRA (F/P) fusion gene; these patients are diagnosed as F/P-mutated myeloid/lymphoid neoplasms with eosinophilia (MLN-eo). Areas covered: This review discusses the results of IM treatment in HES depending on mutation status. The literature on IM therapy in HES by searching PubMed for the terms 'imatinib mesylate', 'hypereosinophilic syndromes' and 'FIP1L1-PDGFRA' has been reviewed. The author's publications as well as his own experience in the field of HES treatment remain a significant contribution to this work. Expert commentary: Imatinib mesylate, a first generation tyrosine kinase inhibitor, has revolutionized the therapeutic approach to patients with hypereosinophilic syndromes and detectable F/P fusion gene. The response to IM in F/P-mutated MLN-eo is universal with minimal side effects. IM at 100mg per day induces complete molecular remission and even lower doses can be efficient to maintain durable response. Some patients may remain in continued remission after IM discontinuation. Resistance to IM is associated with dismal prognosis. IM is less effective in F/P-unmutated HES with short-lived response.