Prenatal and postnatal exposure to traffic-related air pollution (TRAP) and childhood cancer: Systematic review and meta-analysis

Previous studies have suggested a possible link between traffic-related air pollution (TRAP) and the risk of childhood cancers, though findings remain inconsistent. This systematic review and meta-analysis aimed at evaluating the association between TRAP exposure and childhood cancer risk, focusing on prenatal and postnatal exposure to fine particulate matter (PM 2.5 ), nitrogen dioxide (NO 2 ), and benzene. Peer-reviewed manuscripts were identified through PubMed (n=1,116), Web of Science (n=578), and Cochrane Library (n=163) databases through June 21, 2024. Five reviewers independently screened titles, abstracts, and full texts for eligibility. A meta-analysis was conducted, with subgroup analyses based on exposure period (prenatal vs. postnatal) and age group. Results are presented as odds ratios (ORs) and 95% confidence intervals (CIs) per 10 μg/m 3 increase in PM 2.5 and NO 2 exposure, and per 1 μg/m 3 increase in benzene exposure. Of 1,632 studies screened after duplicate removal, 25 met the inclusion criteria. The findings indicated an elevated risk of acute lymphoblastic leukemia (ALL) in children exposed to PM 2.5 (OR: 1.29, 95% CI: 1.01–1.63; 5 studies; I 2 = 72.1%), and increased risks of all childhood cancers (OR: 1.12, 95% CI: 1.02–1.22; 4 studies; I 2 = 0.0%) and acute myeloid leukemia (AML, OR: 1.22, 95% CI: 1.02–1.46; 4 studies; I 2 = 0.0%) associated with benzene exposure. PM 2.5 exposure was also associated with a higher risk of retinoblastoma (OR: 1.68, 95% CI: 1.16–2.43; 3 studies; I 2 = 0.0%). Subgroup analyses revealed a stronger association between postnatal TRAP exposure (PM 2.5 and NO 2 ) and leukemia risk compared to prenatal exposure. This study provides evidence of a link between TRAP exposure and increased childhood cancer risk, particularly during the postnatal period. Further research is needed to confirm these findings.