Purpose: To review the childhood risk factors for pediatric cancer (diagnosis before age 20). Methods: We conducted literature searches using Ovid Medline and Scopus to find primary research studies, review articles, and meta-analyses published from 2014 to 3 March 2021. Results: Strong evidence indicates that an array of genetic and epigenetic phenomena, structural birth defects, and chromosomal anomalies are associated with an increased risk of various childhood cancers. Increased risk is also associated with prior cancer, likely due to previous treatment agents and therapeutic ionizing radiation. Convincing evidence supports associations between several pediatric cancers and ionizing radiation, immunosuppression, and carcinogenic virus infection both in healthy children and in association with immune suppression following organ transplantation. Breastfeeding and a childhood diet rich in fruits and vegetables appears to reduce the risk of pediatric leukemia but the evidence is less strong. Childhood vaccination against carcinogenic viruses is associated with a lower risk of several cancers; there is less strong evidence that other childhood vaccinations more broadly may also lower risk. Ultraviolet (UV) radiation is associated with increased melanoma risk, although most melanomas following childhood UV exposure occur later, in adulthood. Evidence is weak or conflicting for the role of body mass index, other childhood infections, allergies, and certain treatments, including immunomodulator medications and human growth therapy.

Purpose: To achieve a better understanding of the environmental factors that contribute to childhood cancers, so as to inform future prevention efforts. Methods: We conducted a comprehensive review of epidemiological studies on environmental risk factors and childhood cancer, which was published between January 2014 and March 2021. Potential exposure sources presented in this review include air pollution, radiation, and parental occupational exposures. We considered exposures during childhood and parental exposures occurring before the child’s conception and during pregnancy in relation to all types of childhood cancer. Results: Aggregated evidence is strong for associations between leukemia and parental/child exposure to traffic pollution, indoor paints, residential pesticides, and parental occupational/nonoccupational exposure to benzene. Evidence is also strong for associations between brain cancer and residential pesticides and parental occupational exposure to agricultural pesticides. Evidence of associations between leukemia and ionizing radiation from radon and nuclear power plants remains mixed, as does evidence of a link between electromagnetic fields (EMFs) and childhood leukemia. Conclusions: Clear associations have been demonstrated between childhood cancer and environmental factors, including parent/child exposure to traffic pollution, occupational/nonoccupational benzene, indoor paints, residential pesticides, and parental occupational exposure to agricultural pesticides. These associations can be used to inform further study of interventions and public health campaigns to reduce risk.

Purpose: To review parental pre-pregnancy and pregnancy exposures in relation to pediatric cancer (diagnosis before age 20). Methods: We conducted literature searches using Ovid Medline and Scopus to find primary research studies, review articles, and meta-analyses published from 2014 to 17 March 2021. Results: Strong evidence links increased risk of childhood cancer with maternal diabetes, age, and alcohol and coffee consumption during pregnancy. Both paternal and maternal cigarette smoking before and during pregnancy are associated with childhood cancers. Diethylstilbestrol (DES) exposure in utero has long been known to be causally associated with increased risk of vaginal/cervical cancers in adolescent girls. More recent evidence implicates in utero DES exposure to testicular cancer in young men and possible intergenerational effects on ovarian cancer in the granddaughters of women exposed to DES during pregnancy. There is strong evidence that childhood cancer risk is also associated with both high and very low birth weight and with gestational age. Evidence is also strong for the protective effects of maternal vitamin consumption and a healthy diet during pregnancy. Unlike early studies, those reviewed here show no association between in utero exposure to medical ionizing radiation, which may be explained by reductions over time in radiation doses, avoidance of radiation during pregnancy, and/or by inadequate statistical power to detect small increases in risk, rather than a lack of causal association. Evidence is mixed or conflicting for an association between childhood cancer and maternal obesity, birth order, cesarean/instrumental delivery, and prenatal exposure to diagnostic medical radiation. Evidence is weak or absent for associations between childhood cancer and multiple gestations or assisted reproductive therapies, as well as prenatal exposure to hormones other than DES, and medications.