The Relationship between Air Pollution and Brain Cancer: A Systematic Review and Meta-Analysis

BACKGROUND: There is very little epidemiological evidence on the effects of ambient air pollution on brain tumor risk. The purpose of this study was to determine the relationship between exposure to air pollution and the incidence of brain tumors. METHODS: A comprehensive literature search in five international databases, including PubMed/Medline, ProQuest, Scopus, Embase, and ISI/WOS on April 15, 2019, was conducted. The methodology of the present study was based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) statement. The Newcastle-Ottawa Quality Assessment Form was used to evaluate the quality of the selected papers. RESULTS: Five studies that measured adult brain tumors as well as their long-term exposure to at least one of the pollutants criteria for air pollution, PM(2.5) absorbance, and proximity to traffic (Trafnear) were reviewed. The results showed that the pooled relative risk (RR) for incidence of brain tumor and long term exposure to Trafnear, PM(2.5), PM(2.5) absorbance, O(3) and NOx were RR = 1.07, (95% CI 0.99–1.16), P = 0.079, for Trafnear; RR = 0.90, (95% CI 0.80–1.00), P = 0.064 for PM(2.5); RR = 1.63, (95% CI 1.04–2.55), P = 0.031 for PM(2.5) absorbance; RR = 1.3, (95% CI 1.03–1.6), P = 0.023 for O(3); and RR = 1.16, (95% CI 0.93–1.45), P = 0.173 for NOx. Exposure to other air pollutants had no statistically significant association with brain tumor incidence. CONCLUSION: The results showed that exposure to air pollutants, such as O(3) and PM(2.5) absorbance, had the highest correlation with brain tumor incidence. They also showed an absence of correlation between exposure to certain pollutants (SO(2), CO, NO(2), PM(10), PM(2.5)) and brain tumor incidence.