RUNX1 and acute lymphoblastic leukemia: To further characterize the genomic complexity of the unusual iAMP21‐ALL, we performed mate‐pair sequencing (MPseq) on seven cases (5 unusual iAMP21‐ALL and 2 typical iAMP21‐ALL), focusing on those cases with evidence of a RUNX1 signal observed on a chromosome other than chromosome 21 (Figure 2B).