Cytogenetic studies include fluorescence in situ hybridisation (FISH) [26] assays for recurrent gene fusions, rearrangements and amplifications (ETV6-RUNX1; BCR-ABL1; KMT2A rearrangements; other ABL-class rearrangements; intrachromosomal amplification of chromosome 21 [iAMP21]; TCF3-HLF) and screening for aneuploidies (specifically hypodiploid ALL, modal chromosome number < 40) by DNA ploidy analysis (flow cytometry) and/or conventional karyotyping. Here, ABL1 is linked to acute lymphoblastic leukemia.