EFS of patients treated on UK MRC ALL97 by cytogenetic subgroup. iAMP21 indicates intrachromosomal amplification of chromosome 21q; t(12;21), t(12;21)(p13;q22)/ETV6-RUNX1; HeH, high hyperdiploidy (51-65 chromosomes); t(9;22), t(9;22)(q34;q11)/BCR-ABL; 11q23, 11q23/MLL translocation; less than 40 chromosomes (chrs), near-haploidy (23-29 chromosomes), or low hypodiploidy (30-39 chromosomes); and other, all other patients.