Next, to investigate whether other frequently occurring lesions in E::R-positive childhood pB-ALL similarly increased the leukemia incidence, we mutated the zebrafish ortholog of the human CDKN2A/B gene in the E::R knock-in zebrafish line, as the CDKN2A/B gene is also affected by deletions in 25% of children with E::R-positive leukemia [15,16]. Here, CDKN2A is linked to acute lymphoblastic leukemia.