CRLF2 and acute lymphoblastic leukemia: While Ph-like ALL has a high incidence (60%) of genomic rearrangements leading to an increased expression of the receptor to the cytokine TSLP, CRLF2 [17], and more than half of these have mutations in JAK and IL7R pathway - including constitutionally activating JAK2 mutations [11, 18, 19], less than 10% of Ph-like ALL also acquire RAS/MAPK pathway mutations.