Our estimate of the current burden in 2005 of occupation-related cancers of 5.3% translates to over 8000 cancer deaths in GB and is in contrast to the 212 deaths due to occupational injuries that occurred in 2005/06 (HSE, 2006
). Burden estimates from other studies range between 3 and 10%, partly due to differences in the numbers of cancers and carcinogens considered. The study has identified several industry sectors and occupations with high numbers of attributable cancer deaths and registrations including construction, metal working, personal/household services, mining, land transport, printing/publishing, retail/hotels/restaurants, public administration/defence, farming and several manufacturing sectors (Hutchings and Rushton, 2012b
). The construction industry and agriculture and farming together contributed 43% of the fatal injuries reported in 2005/06 (HSE, 2006
), and our study adds to the work-related concerns in these industries, both of which also have the potential for increased risks from substances associated with respiratory diseases (Rushton, 2007
The results presented in this supplement must be considered taking into account several uncertainties and limitations. Agents classified by IARC by the end of 2008 as Group I and 2A carcinogens were assessed. Other substances, such as IARC group 2B carcinogens, many of which may be treated as if they were human carcinogens in regulatory settings, have not yet been evaluated; our estimates could thus be too low. In addition, our estimates do not include evaluation of the results from the review and update by IARC of all Group 1 carcinogens carried out in 2009, in which a separate classification (potentially varying) was given for all cancer sites that were relevant to specific carcinogens. Our estimates are thus almost certainly an underestimate of the true burden.
The assumptions made in the methodology used for this study may have introduced uncertainty or bias in the estimates. For example, studies of British workforces were not always available from which to choose appropriate risk estimates; the study chosen may not have reflected exposures experienced in GB; and there may have been differences in distributions of confounders. However, it should be noted that the majority of risk estimates were obtained from meta-analyses, pooled studies or reviews. There was a paucity of available information on risk estimates for women, and for many carcinogens the risk estimates for men were used for women. In addition, most estimates were for mortality rather than for incidence. Epidemiological studies of occupational groups are often confounded by a ‘healthy worker effect', that is, a reduced overall risk estimate compared with the general population. This, together with potential misclassification of exposure in epidemiological studies, could lead to an underestimation of the true effect and thus an underestimation of the burden.
The approach to subdividing industry sectors into ‘high' and ‘low' exposure and allocating suitable risk estimates was a response to the lack of data on proportions exposed at different levels of exposure and the fact that many studies of occupational groups use relatively simple approaches to exposure assessment, for example, job titles. For most of the carcinogens considered, risk estimates in the source studies were related to some estimate of cumulative exposure. In assigning ‘higher' and ‘lower' categories to the industry groups for the calculation of the proportions exposed, e.g., using CAREX, implicit assumptions were made regarding the similarity of durations and intensities of exposure between the source and target (national) populations. Where no risk estimate could be identified for low levels of exposure, we estimated a relative risk (RR) based on harmonic mean of the high/low ratios across all other cancer–exposure pairs in the overall project where data were available; if the resulting RR estimate was <1, RR was set to 1. This may have led to inaccurate risk estimates for the low categories (either too large or too small). A substantial proportion of the ANs is likely to have resulted from a large number of workers with low exposures.
Our figures could have underestimated the number of workers ‘ever exposed' in the REP because workers with <1 year of employment were not included in the analysis consistent with the exclusion of short term workers in many occupational epidemiological studies. Inclusion of these would have increased the numbers ever exposed considerably and hence increase the AFs and numbers.
There is a general paucity of information on latency of cancers due to occupational carcinogens, and hence we made pragmatic assumptions about the length of the latency period and hence the REP. This resulted in high estimates in some situations.
Work is ongoing to explore the sensitivity of the estimates to the sources of uncertainty and bias discussed above. An important aspect throughout this project was the involvement of international experts, including IARC, in advising on the methodology and interpretation of the results and peer reviewing the many technical reports. This supplement, together with the detailed technical reports on the HSE website, facilitates the transparent presentation of the methodology, data and results from this project. These methods have the potential to be adapted for use in other countries and extended to include social and economic impact evaluation. For example, the methodology and results contained in this study are informing an on-going estimation of occupational cancer for the Global Burden of Disease programme undertaken by the World Health Organisation.