 Previous findings have shown that a biomarker comprised of the three microRNAs miRs miR-451, miR-151-5p and miR-1290 can independently predict precursor B-cell acute lymphoblastic leukemia B- ALL patients risk for relapse when measured in cells from a bone marrow BM aspiration taken at diagnosis Avigad et al., 2016: Genes, Chromosomes Cancer 55:328-339. Curewize Health recognizes that the development of a minimally invasive blood test for frequent long-term monitoring can greatly benefit pediatric precursor B-ALL patients. Therefore, the current study will investigate the monitoring ability of miR-451, miR-151-5p and miR-1290 measured in blood samples. The study will be performed in two stages: 