STAT5B and acute lymphoblastic leukemia: In addition, no association between N642H mutation activating STAT5B, abnormality recently identified in T-ALL and associated with a higher risk of relapse, [12] and CRLF2 over-expression was observed (0/4 STAT5B N642H positive among CRLF2-high patients and 1/35 among CRLF2-low patients).