[A man with oral ulcers caused by hypereosinophilic syndrome and a good response to the tyrosine-kinase inhibitor imatinib].

For the last 2 years, a 55-year-old man had painful, recurrent oral ulcers. Histological examination showed non-specific inflammation. Eosinophilia in the blood and bone marrow raised the suspicion of hypereosinophilic syndrome. No other specific organ involvement was observed. The diagnosis was confirmed by detection of the fusion gene 'FIP1-like-1-platelet-derived growth factor receptor alpha' (FIP1L1-PDGFRA) in the peripheral blood and bone marrow. Treatment with the tyrosine-kinase inhibitor imatinib resulted in a rapid response that has been maintained for more than 2 years. Hypereosinophilic syndrome is a rare haematological disorder. Until recently diagnosis was made by exclusion, and the course of disease was often fatal. Fusion of the FIP1L1 gene to the PDGFRA gene was identified recently in some patients with hypereosinophilic syndrome. The fusion results in a novel tyrosine kinase that is constitutively activated and may induce proliferation ofhaematopoietic cells. Treatment with imatinib targets this tyrosine kinase. These advances in our understanding of the molecular biology of the disease will lead to a new classification of hypereosinophilic syndrome with specific therapeutic options.