JAK2 and acute lymphoblastic leukemia: A high prevalence (16 of the 22, 72.7%) of IKZF1 deletion in these patients was also confirmed in our study, suggesting that kinase fusion-positive BCP-ALL patients are biologically similar to Ph+ ALL patients.22 However, JAK2 mutation was present in only 2 (16.7%) of the 12 patients with CRLF2 rearrangements, which was a lower rate than that (55%) reported in previous studies.5 The reason for this discrepancy is unclear.