Summary: Traffic-related air pollution and prostate cancer risk: a case-control study in Montreal, Canada
Marie-Élise Parent, Mark S Goldberg, Dan L Crouse, Nancy A Ross, Hong Chen, Marie-France Valois, Alexandre Liautaud
The geographical variations in prostate cancer occurrence are one of the most puzzling aspects of the disease to researchers. This is because there is currently a lack of information on modifiable environmental risk factors for prostate cancer. Without this knowledge, it is impossible to prevent cases that might not have to happen. While a handful of studies have examined the relationship between ambient air pollution and prostate cancer, the study by Marie-Elise Parent, Mark Goldberg, Dan L. Crouse, Nancy A. Ross, Hong Chen, Marie-France Valois, and Alexandre Liautaud is the first to observe an association between exposure to traffic-related air pollution in particular and prostate cancer incidence. Indeed, they found that there is a 27% higher risk of prostate cancer for every increase of 5 parts per billion of nitrogen dioxide in an area. This means that if the air is divided into a billion parts, we are concerned for the difference of 5 of those parts. While this may seem tiny, humans start to feel irritated by nitrogen dioxide once concentrations reach 100 parts per billion.
To arrive at these results, the researchers made use of a survey conducted in Montreal of the 2005-2006 outdoor air concentrations of nitrogen dioxide (NO2) – a marker for traffic-related air pollution – to develop a map of the concentrations. They then linked them to the addresses of 803 men with prostate cancer at the time of their diagnosis and at the time of interview for the 969 men who acted as controls. NO2 was used because local traffic caused by vehicles is a main contributor to overall air pollution. Moreover, vehicles emit many different kinds of chemicals and compounds, some of which are known carcinogens, and long-term exposure to outdoor air pollution has been associated with several health problems.
With these novel and surprising results, which were also sensitive to the effects of age, first-degree family history of prostate cancer, ancestry, and attained level of education – all factors associated with prostate cancer risk – spatially referenced data can now be seen as a potentially fruitful avenue for research. These findings must be replicated, though, and with more precise data regarding residential history and NO2 exposure, before they can be interpreted with certainty. As a consequence of approximations made with the data, it is possible that these results underestimate the true risk of prostate cancer associated with exposure to air pollution in this population. It is also likely that the present findings reflect an association with the complex mixture of compounds that come from car exhaust, and not merely the NO2 itself. Should traffic-related air pollution indeed prove to be causal, it could explain a large proportion of new cases. It is thus essential that other independent studies be conducted.