Recently, IKZF1 deletions have been shown to be associated notonly with the leukemogenic process but also to confer a poor prognosis in allrisk groups of B-cell precursor ALL. In a previous study, we used Multiplex Ligation-dependentProbe Amplification (MLPA) to investigate the presence ofIKZF1 deletions in bone marrow DNA from 116 children diagnosed with BCPALL in a single center and treated according to NOPHO protocols. Deletionswere detected in 16% of cases; both event free survival and overall survivalwere significantly reduced in the IKZF1-deleted group compared to the groupwith intact IKZF1.