Heat-map analysis in 206 children and young adults with high-risk precursor B-ALL treated in COG study 9906. The R1 cohort captured all patients with MLL rearrangements and the R2 cohort captured all patients with the t(1;19). The R8 cohort was found to have BCR-ABL–like signature,³² CRLF2 mutations, and a poor outcome. Other mutations involving JAK were identified, suggesting that this cohort might respond to tyrosine kinase–directed therapy. The remaining R cohorts have molecular anomalies that remain undefined. (Used with permission from Harvey et al.³³ )