ediatric cancer is rare, with fewer than 10,000 solid tumors diagnosed in children annually in the United States 1. Previous studies interrogating germline predisposition broadly across pediatric cancer types have found heritable germline predisposition in 8-12% of patients. The yield of germline predisposition detected is dependent on the genes included for analysis and variant interpretation as well as the ascertainment biases found in each cohort. Iterative data are required to expand upon the understanding of susceptibility to pediatric cancer and determine the extent to which germline data may translate into clinical practice 2-7. Certain pediatric cancer diagnoses have well-established associations with germline mutations in specific genes and should automatically prompt clinical suspicion of a cancer predisposition, for example, retinoblastoma (RB1), pleuropulmonary blastoma (DICER1), optic pathway glioma (NF1), atypical teratoid/rhabdoid tumors (SMARCB1), small cell hypercalcemic ovarian tumors (SMARCA4), adrenal cortical tumors (TP53) and hypodiploid acute lymphoblastic leukemia (TP53) 8-10. Germline testing can also be critical for distinguishing between conditions like neurofibromatosis type 1 (NF1) and constitutional mismatch repair deficiency (CMMRD), which can be phenocopies of each other. For example, a child presenting with numerous café au lait spots and leukemia may have either of these conditions, but treatment and screening recommendations for the proband and family members will differ depending on the germline diagnosis 11. Besides the known associations of causal germline mutations, broad tumor-normal sequencing has revealed novel associations 9,12. While some of these findings likely represent population detection and do not play a role in the pathogenesis of the cancer in question 13 , other novel associations are likely causal. Population detection