ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by BCR-ABL, a chimeric gene generated as a result of a reciprocal translocation [t(9;22)(q34;q11), cytogenetically visible as the Philadelphia chromosome (Ph)] that places sequences from the ABL gene from chromosome 9 downstream of the BCR gene on chromosome 22.