Chronic myeloid leukemia (CML) is characterized by the BCR–ABL1 fusion gene mutation whereas polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF) are typically characterized by the presence of JAK2, CALR, or MPL gene mutations [271]. Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.