Correlation Between Nitrogen Dioxide as an Air Pollution Indicator and Breast Cancer: a Systematic Review and Meta- Analysis

Background: The aim of this systematic review was to study the relationship between exposure to nitrogen dioxide (NO2) in the ambient air and breast cancer incidence. Materials and
Methods: A systematic review was performed based on the MOOSE guideline for review of observational studies. We searched five online databases (PubMed, Science Direct, Google Scholar, EBSCO, and Scopus) from their conception to June 2014. A pooled estimate of the correlation between NO2 exposure and breast cancer incidence was calculated using Pearson’s correlation coefficient.
Results: A total of 654 titles were retrieved in the initial search of the databases. Further refinement and screening of the retrieved studies produced a total of five studies from four countries. The studies included three ecological studies (aggregate level) and two individual based studies (one prospective cohort and the other one a case-control study). The ecological studies were pooled and the meta-analysis of correlation coefficient without z transformation showed a pooled estimate of r = 0.89 with 95% CI of 0.84 to 0.95. Using z transformation, the pooled r was 1.38 with 95%CI of 1.11 to 1.59. No significant heterogeneity between studies was observed. Following a sensitivity analysis and the removal of each study from pooled analysis we did not see any significant change in the pooled estimate.
Conclusions: It was concluded that there is a tendency toward a weak association between exposure to NO2 in ambient air and breast cancer at the individual level and a significant association at the aggregate level.