Diagnostic blood or bone marrow samples from patients with T-cell acute lymphoblastic leukemia treated in the FRALLE200T or GRAALL03-05 trials containing ≥70% lymphoblasts were assayed via SNP microarray. Gain of MLLT4, deletion of CREBBP, and ≥15 genomic imbalances were found to be independently prognostic of EFS in a multivariate analysis in the study cohort. EFS, event-free survival; SNP, single-nucleotide polymorphism.