In 2001 Schaller et al reported the first case of a patient with HES resistant to conventional treatment that responded to imatinib mesylate. (Schaller, MGM 2001). After that, many authors described cases with hypereosinophilia that achieve a rapid response to Imatinib and in 2003 Cools et al identified a novel tyrosine kinase generated from the fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFRalfa gene associated to hypereosinophilia.