Abstract
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. 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. 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. 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.
Highlights
Breast cancer is a leading cause of mortality and morbidity all over the world
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
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% confidence intervals (CIs) of 0.84 to 0.95
Summary
Breast cancer is a leading cause of mortality and morbidity all over the world. In 2008, close to 1.4 million cases were diagnosed with breast cancer worldwide (Ferlay et al, 2007). Several studies have reported higher mortality rates for breast cancer in areas with a high degree of air pollution (Chen and Bina, 2012a; Wei et al, 2012; Al-Ahmadi and AlZahrani, 2013). The main gaseous compounds are nitrogen oxides (NOx), carbon oxides (COx), sulfur oxides (SOx) and the solid particles include particulate matter with diameters of less than 10 μm (PM10). Many of these compounds either solid or gas have been proven to be either mutagenic or carcinogenic and can cause cancer (Lewtas, 2007). Data extraction For each selected study the following data or items of information were abstracted and tabulated for further analysis: first author identifier; date of publication; date
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