ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Among 7 CML cases with a "masked Ph" chromosome, 3 showed the 5'BCR/3'ABL1 fusion signal on 22q11, the second breakpoint on the derivative chromosome 22 mapping inside chromosome 9 sequences distal to the ABL1 gene (Table 1; Fig. 1C).