CRLF2 and precursor B-cell acute lymphoblastic leukemia: Whereas a 2016 report defined five subgroups (11), a more recent review from the Mullighan group (1) subdivided Ph-like B-ALL into four groups: (1) JAK family activating, including rearrangement of cytokine receptors (CRLF2, EPOR, IL2RB) and/or JAK mutations: (2) ABL-class including rearrangements of ABL1, ABL2, PDGFRA, PDGFRB, or CSF1R; (3) Other kinase, including FLT3 and NTRK3; (4) RAS signaling, including mutations in NRAS or KRAS. The relative frequency of genetic alterations differs between pediatric and adult patients with Ph-like B-ALL.