ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Approximately 5% of all CML or ALL patients are diagnosed with rare BCR-ABL1 rearrangements that involve fusion of alternative exons, insertions, or breakpoints within exons such as e19a2 (the most common rearrangement), e8a2, e13a3, e14a3, e1a3, and e6a2.