Ideas about the cause of lung cancer have been so dominated by recognition of the effect of smoking for the last forty years that it is sometimes easy to forget that there may be other important causal factors and that lung cancer still occurs in non-smokers. The effect of smoking is so strong that it can be quite difficult to unravel other causes, because the presence of a few smokers in any group will so alter the statistics. However, there are undoubtedly other factors at work in the development of lung cancer and many of them can now be judged.
Once suspicion has been cast on an occupation it is a relatively straightforward, although laborious, task to examine the risk by comparing the incidence of lung cancer in workers in that occupation with that of the general population, and then doing more detailed work to look at the effect of the number of years spent in the occupation or the dose of the suspected agent to which the workers are exposed. Occupational hazard of lung cancer has been shown to be present for workers with asbestos, chrome, hydrocarbon chemicals in the old-style coke and gas industries, some chemicals used in the paint industry and for those who mine uranium (who are probably affected by radon gas from the rocks). New and effective regulations have been brought in to control these industries and the risks have been substantially reduced or eliminated. Careful monitoring remains necessary. Less certain risks have been suggested for workers with cadmium, nickel and vinyl chloride, and some fibres used in the textile industries, and precautions are now taken in industries based on these substances. Butchers appear to have a very small excess of lung cancer over the level which might be predicted. This is entirely unexplained and appears to be independent of smoking habits.