A rare form of leukemia known as TCF3::HLF-positive B cell acute lymphoblastic leukemia (B-ALL) sits among the most aggressive blood cancers seen in children. The disease causes a rapid buildup of abnormal blood cells, but unlike other types of leukemia, it also severely damages bones and causes pain. To make things worse, patients with TCF3::HLF-positive B-ALL tend to relapse quickly after treatment, with survival rates remaining low.