ABL1 and acquired polycythemia vera: Essential thrombocythemia (ET) and polycythemia vera (PV) are BCR-ABL–negative myeloproliferative neoplasms (MPN) characterized by an overproduction of mature blood elements, tendencies toward thrombosis and hemorrhage, extramedullary hematopoiesis (mild splenomegaly), and transformation to overt myelofibrosis (MF)/acute myeloid leukemia (AML) [1, 2].