IL3 and B-cell acute lymphoblastic leukemia: In a subset of (mostly pediatric) patients with B cell acute lymphoblastic leukemia, a specific translocation, t(5;14)(q31;q32), leads to juxtaposition of the IgH enhancer and the IL‐3 gene, resulting in (over)production of IL‐3 by leukemic cells; these patients may also present with (reactive) HE.