8 chromosomes defined modal number by iFISH can prognostically stratify B-pALL. Modal number of ≥ 55 relates significantly to better outcome of hyperdiploid B-pALL. Hyperdiploid B-pALL with ≥ 55 chromosomes reveals less complex subclonal landscape. Highly conserved chromosomal gain is a unique feature of high hyperdiploid B-pALL. Conserved hierarchical gain of chromosome 4 is an independent prognostic factor.