IKZF1 and acute lymphoblastic leukemia: A study of 991 B-ALL patients in the AIEOP-BFM ALL 2000 trial identified a high-risk group, IKZF1plus, characterized by the co-occurring of IKZF1 deletions with PAX5, PAR1, CDKN2A, or CDKN2B deletions (excluding ERG deletion).