During the past decade, the tyrosine kinase inhibitor (TKI) imatinib has been successfully used for the treatment of patients with BCR/ABL1+ chronic myeloid leukemia (CML) and for the treatment of FIP1L1/PDGFRA+ chronic eosinophilic leukemia (CEL) [32-36]. The gene discussed is BCR; the disease is Chronic Eosinophilic Leukemia, Not Otherwise Specified.