BCR and essential thrombocythemia: Essential thrombocythemia, PV, and PMF are clonal disorders, which most commonly stem from mutations in JAK2, CALR, or MPL. 7Chronic myeloid leukemia, on the other hand, is characterized by fusion of the Abelson murine leukemia (ABL) gene with the breakpoint cluster region (BCR), t(9;22) (q34;q11).