Low penetrance common genetic variations, for instance in CEBPE, IKZF1, and ARID5B genes in ALL, are associated with cancer risk and may also contribute to familial concordance as combinations of low-frequency alleles or ‘polygenic risk scores’ have been shown to be as impactful as single strong predisposition mutations in adult cancers (Fantus and Helfand, 2019; Yadav and Couch, 2019); however, their contribution to cancer clustering among children and their families has not yet been studied. This evidence concerns the gene CEBPE and acute lymphoblastic leukemia.