INTRODUCTION
Hypereosinophilic syndrome (HES) is a rare disease with a heterogeneous presentation. It is defined by a blood hypereosinophilia greater than or equal to 1.5 G/L and/or tissue hypereosinophilia of prolonged evolution (more than 1 month) associated with tissue damage related to eosinophil toxicity. There are 4 main types of HES: clonal HES, including chronic eosinophilic leukemia, secondary or associated HES including lymphoid HES, familial HES, and idiopathic HES.
Clonal HES may present a molecular abnormality of the PDGFRA, PDGFRB, FGFR1 genes, in particular the FIP1L1-PDGFRA fusion resulting from the 4q2 deletion, a transcript present in myeloid neoplasia with FIP1L1-PDGFRA-related hypereosinophilia. These are particularly sensitive to a tyrosine kinase inhibitor, Imatinib, which has improved their prognosis.
As with chronic myeloid leukemia (CML) in sustained molecular complete remission (CMR) after discontinuation of TKIs, discontinuation of Imatinib in FIP1L1-PDGFRA-positive HES is being evaluated. But unlike CML, where TKI discontinuation is guided by specific recommendations, in HES, because of the smaller number of cases, discontinuation is done on a case-by-case basis. Here we report a case of FIP1L1-PDGFRA-positive HES in sustained CMR after Imatinib discontinuation.