CRLF2 and precursor B-cell acute lymphoblastic leukemia: CRLF2 overexpression contributes to a poor prognosis and occurs in 5–15% of all patients with B-ALL, 50–60% of pediatric B-ALL patients with Down syndrome, and 50% of genetic alterations in Philadelphia-like ALL (Ph-like ALL), another high-risk B-ALL subtype [7,8,9,10,11,12,13].