Workplace and cancer: interactions and updates.

Occupational and environmental hazards and the potential adverse health effects arising from them are an area of increasing public interest and a topic of a large body of research within many different disciplines. Investigation involves both knowledge of the source and nature of the hazard and an understanding of the relationship of the exposure to the disease. Epidemiological studies of industrial workforces have played an important role in the identification of carcinogens and the understanding of the aetiology of cancer. A distinction is often made between conditions from which individuals may have no or only partial control and those for which some element of personal choice exists. Exposures encountered at work would tend to fall in the former category, while ‘lifestyle’ factors such as smoking, eating a high-fat diet and drinking alcohol would come in the latter. The working environment should not be a place where there is a risk of disease or injury, yet many thousands of workers worldwide are exposed to hazardous substances at work everyday. Although substances related to occupational cancer are often associated with chemical exposures, especially manmade [1], a wider definition is needed to encompass all patterns of working. The International Agency for Research into Cancer (IARC) classifies substances into four groups according to the evidence as shown in Table 1 (http://monographs. iarc.fr/ENG/Preamble/index.php, accessed July 2008). For human data, sufficient evidence is defined as the establishment of a causal relationship between exposure to the agent and human cancer. Limited evidence is defined as the observation of a positive association between exposure to the agent and human cancer, for which a causal interpretation is considered credible, but chance, bias or confounding could not be ruled out with reasonable confidence. Similar definitions relate to the evidence from experimental data. Since 1972, IARC has published 92 volumes as part of their monograph programme, with a further seven in press, that report the evaluation by groups of international experts of the carcinogenicity of . 900 substances, complex mixtures and industrial processes. Of these, 400 have been classed as carcinogenic (Group 1 or 2A) or potentially carcinogenic to humans (Group 2B). In a review of the IARC monograph series through 2003 [2], and in subsequent monographs (published and unpublished), some 31 definite (IARC Group 1) and 32 probable (IARC Group 2A) human occupational carcinogens have been defined for . 20 cancer sites. The results from studies of occupational groups have many uses, for example in carrying out risk assessments for standard setting and for decisions regarding compensation. There is also an increasing interest in estimating and comparing burdens of disease generally [3] and for cancer [4,5]. Estimates can identify major risk factors and high-risk populations, support decisions on priority actions for risk reduction and provide an understanding of important contributions to health inequalities. Nearly 30 years ago, Doll and Peto [6], in their report to the US Congress, presented a method of estimating the effects of different factors on cancer mortality in the USA; their estimate for occupational factors was 4% of all US cancer deaths with an uncertainty range of 2–8%. These figures have been used by the Health & Safety Executive (HSE) to inform their strategy for chemicals and other agents that may cause occupational cancer. Since 1981, there have been several other estimates of attributable occupational cancer burden some of which are shown for selected cancers in Table 2 [6, 12]. The second row of the table gives recent estimates by Rushton et al. [7] from an ongoing study to update the Doll and Peto figures for Great Britain (GB). Some of the differences between the results can be explained by differences in the numbers of agents considered. For example, Steenland et al. [10] estimate the burden of lung cancer for eight occupational carcinogens compared to 19 in the British study [7]. Other differences may be due to differences between countries in the occupational situations in which exposures occur. Different methodological approaches were also used for some of the studies in the table. However, although the magnitude of the burden differs between studies, the patterns are generally similar. These percentages can translate into considerable numbers of deaths and cancer registrations. For example, the World Health Organization estimate every year that at least 200 000 people worldwide die from cancer related to Department of Epidemiology and Public Health, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.