CRLF2 and acute lymphoblastic leukemia: It is worth noting that we observed expression of Ik6 in 18.5% of B-ALL without CRLF2 rearrangement and particularly that 75.0% of these IK6+ patients also showed overexpressed CRLF2. These data indicate that IKZF1 deletion with CRLF2 over expression but no CRLF2 rearrangement may distinguish a subgroup of adult ALL patients with unfavorable prognosis.