ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia is a clonal myeloproliferative disorder characterized by the reciprocal translocation t(9;22)(q34;q11), involving the proto-oncogene ABL1 (Abelson leukemia kinase proto-oncogene) on chromosome 9 and the BCR (breakpoint cluster region) on chromosome 22.