Chronic myeloid leukemia (CML) and acute lymphocytic leukemia (ALL): Reciprocal translocation t(9;22)(q34;q11) leads to a hybrid BCR-ABL1 gene encoding a fusion protein with increased tyrosine-kinase activity. This protein is directly responsible for the transformation of leukemic cells. CML: Approximately 95% of CML are BCR-ABL1 positive. ALL: A fusion gene BCR-ABL1 is present in about 25% of adult patients and 5% of children. The presence of BCR-ABL1 in ALL is associated with a poor prognosis.