JAK2 and acute lymphoblastic leukemia: It is unclear why JAK2 alterations are predominantly identified within B-ALL rather than T-cell ALL (T-ALL), although there have been rare reports in T-ALL (Lacronique et al., 1997; Peeters et al., 1997; Cheng et al., 2017; Huang et al., 2020; Kaplan et al., 2021).