Optimal risk stratification and treatment planning require testing marrow or peripheral blood lymphoblasts for specific recurrent gene abnormalities using: (i) fluorescence in situ hybridization (FISH) for recurrent genetic abnormalities; (ii) reverse transcriptase-polymerase chain reaction (RT-PCR) testing for the detection of BCR-ABL1 gene rearrangements, denoting an underlying t (9;22)(q34.1;q11.2)/BCR-ABL1 chromosomal translocation typical of Philadelphia chromosome-positive (Ph+) ALL; and (iii) NGS for gene fusions and pathogenic mutations (13, 14). The gene discussed is ABL1; the disease is acute lymphoblastic leukemia.