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. The gene discussed is ABL1; the disease is acute lymphoblastic leukemia.