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.