In addition, JAK1 and JAK2 mutations are found in approximately half of CRLF2-rearranged Ph-like ALL.12, 13, 14 Preclinical studies have suggested benefit of ruxolitinib for the treatment of Ph-like ALL and CRLF2-rearranged ALL.129, 130 In addition, ruxolitinib inhibited tumor growth in in vitro and in vivo models of T-ALL with a gain of function in IL-7 R-alpha subunit.131 A phase 2 trial of ruxolitinib with standard multi-agent chemotherapy is currently open for recruitment of children, adolescents and adults with newly diagnosed high-risk B-ALL with CRLF2 rearrangements (NCT02723994). Here, JAK1 is linked to precursor B-cell acute lymphoblastic leukemia.