It has also been demonstrated that allelic polymorphisms that affect the production of key effector cytokines, such as IFNγ, can influence the timing of the onset of B-ALL in children, and a subset of pediatric B-ALL patients that relapse and display IL-15 receptor α (IL15Rα) gene expression levels in blasts that are above the median level experience better subsequent event-free and overall survival [39,40]. This evidence concerns the gene IFNG and precursor B-cell acute lymphoblastic leukemia.