ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: In chronic myeloid leukemia (CML), the balanced reciprocal translocation between the long arms of chromosomes 9 and 22 t(9;22)(q34;q11)—forming the “Philadelphia” (Ph’) chromosome through the creation of the BCR-ABL1 fusion gene—promotes leukemic stem cell uncontrolled proliferation.