Lung cancer risk and diesel exhaust exposure

Lung cancer is the leading cause of cancer mortality in many countries, particularly in Western Europe and North America. Smoking is the major cause of lung cancer and numerous chemical compounds, industrial processes, and occupations have been found to carry excess risk for the development of the disease. Diesel engine exhaust was first suggested to be a possible risk factor for lung cancer about thirty years ago. Since that time evidence has accumulated from various sources on the association between diesel engine emissions and unfavourable respiratory effects. Occupational analyses have consistently shown excess lung cancer risk in transport workers, which in a number of studies remains after adjustment for smoking. Follow-up studies of vehicle transport workers in London have not detected any excess risk for lung cancer, while studies performed in the US have found an increased risk. Excess lung cancer risk detected in railroad workers in North America is probably not due to asbestos exposure, however, smoking may contribute to the excess risk detected. Several case-control studies have been published in recent years which have consistently shown a risk greater than one for work in diesel-related occupations in smokers and, more importantly, also in non-smokers. The level of excess risk detected in most studies is around 1.5 and often does not reach statistical significance (due to lack of power). The excess risk required long exposure and/or a long lag time to become evident. Therefor, diesel exhaust does not pose a significant threat to the general population. The population attributable risk however, because of the large numbers of occupations involved, is estimated at nearly 5% of all male lung cancer deaths.