Cancer is caused by a complex interplay of factors. Very often it is difficult to assess the role of occupational exposures in the development of cancer. Furthermore, many solid tumours present themselves many years after (usually at least 10 but in some cases over 25 years) the relevant exposures took place, making the association of disease with such exposures particularly difficult to establish. This means that national records of cancer registrations, deaths and other data sources such as the THOR network or Industrial Injuries Disablement Benefit (IIDB) scheme, do not allow an accurate assessment of the overall number of work-related cancers.
However, it is possible to estimate the number and the proportion of cases of cancer that would not have occurred in the absence of workplace exposures. To do this information about the risk of cancer from workplace hazards relative to the general risk, the numbers of workers exposed to those risks and the total numbers of cases of cancers of interest is required.
In 1981, in their report to the US Congress, Doll & Peto presented an estimate of the effects of occupational exposure on cancer mortality1. They estimated that 4%, with an uncertainty range of 2% to 8%, of cancer deaths in the US were attributable to occupation. For over 25 years since the report, this proportion of attribution has been used as the basis for estimating the burden of occupational cancer in Great Britain. In order to obtain an update estimate to inform the development and prioritisation of control measures, the Health and Safety Executive has commissioned a research study to estimate the burden of occupational cancer specifically for Great Britain. The study has been led by Dr Lesley Rushton from the Imperial College, London, in consultation with national and international experts in epidemiology, cancer and occupational hygiene 2,3.
The cancer burden study has estimated that 8 000 cancer deaths and around 14 000 cancer registrations per year in Great Britain could be attributed to past occupational exposure to known carcinogens4,5. These represented 5.3% (8.2% for men and 2.3% for women) of all cancer deaths recorded in 2005 and 4% (5.7% for men and 2.1% for women) of all cancer registrations in 2004 in Great Britain. This estimate has included both established and probable carcinogens (Table CAN01A) evaluated and classified by the International Agency for Research on Cancer (IARC)6. If the estimate was restricted only to the established carcinogens, the attributable proportion would moderately reduce (Table CAN01B) to 4% for all cancer deaths and 3.4% for all cancer registrations. This estimate indicates that one in every 20 cancer deaths is the result of occupational exposure and is potentially preventable.
Unlike other estimates of cancer burden, the current study in Great Britain has provided quantitative estimates by cancer types, carcinogens and industry sectors to provide relevant information to support prioritisation of preventive actions. This study showed that lung cancer contributes to the largest number of both deaths and registrations of occupational cancer. It was followed by mesothelioma, breast cancer and bladder cancer for cancer deaths; and was followed by non-melanoma skin cancer (NMSC), breast cancer and mesothelioma for cancer registrations (Table CAN01A).
The top ten leading occupational carcinogens identified from the study are listed in table CAN02 ordered according to the number of attributable deaths, and in table CAN03, ordered according to the number of attributable registrations. Asbestos is responsible for the largest proportion of the burden. One in two occupational cancer deaths and one in three occupational cancer registrations were caused by asbestos. In addition, this study has highlighted other major occupational carcinogens, such as silica, diesel engine exhausts (DEEs), mineral oils in terms of their contribution to deaths; and shift working, mineral oils and solar radiation in terms of their contribution to registrations.
Industries that have contributed significantly to the total cancer burden are listed in tables CAN04 and CAN05. Each of the industries listed has contributed to more than 100 cancer deaths or 100 cancer registrations. The construction industry has contributed the most amongst the industrial sectors, with 40% of the occupational cancer deaths and cancer registrations being estimated from this industry. Most of the cancer deaths and cancer registrations in this industry were caused by exposures to asbestos and silica in the past. In addition, in the construction industry, solar radiation, coal tars and pitches were responsible for an additional 1 300 cancer registrations, mostly causing NMSCs.
The overview of the results and a summary of the methodology of the cancer burden study have been presented in separate reports4,7,8. Technical reports for each of the 24 cancer sites are in preparation, which will give more details of the source data, cancer burden calculation, and statistical methodology. These will be available on the HSE website soon.
Work is underway to estimate Disability-Adjusted Life Years lost to occupational cancer. Furthermore, the method used for estimating the current cancer burden will be extended to also estimate the future cancer burden. The research findings will enable HSE to estimate the economic costs of occupational cancer and to develop better ways of reducing occupational cancer in Great Britain.
The International Agency for Research on Cancer (IARC) is part of the World Health Organization. IARC runs a monograph programme evaluating evidence of the carcinogenicity of specific exposures9. The monographs published by IARC are recognized as an authoritative source of information on the carcinogenicity of a wide range of human exposures. National and international authorities have been using this information in making risk assessments and in formulating decisions concerning necessary preventive measures.
Since 1971, the carcinogenicity of more than 900 agents has been evaluated. According to the updated information published by IARC in May 20106, 107 agents have been identified as established human carcinogens (IARC Group 1), 58 agents were probable (IARC Group 2A) and 249 agents were possible (IARC Group 2B) human carcinogens. These categories indicate only the strength of the evidence that exposure to an agent is carcinogenic rather than the level of the carcinogenic risk of the agent. For example, the term "probably" carcinogenic represents a higher level of evidence of human carcinogenicity than the term "possibly".
The specific forms of occupational cancer which are currently compensable under the Department for Work and Pensions Industrial Injuries and Disablement Benefit (IIDB) scheme are listed below:
The number of people compensated for occupational cancer are presented in tables IIDB03 and IIDB05. On average, around 2000 cases per year were compensated in the last five years. The majority of them were asbestos related cancers, such as mesothelioma (D3) and other asbestos related lung cancer (D8 and D8A). The number of people compensated for non-asbestos related cancers (i.e. D6, C23 and C24) was relatively small and has typically been around 50 or fewer cases in total per year. Of the asbestos related cancers, many mesothelioma cases are now compensated, but only a small proportion of cases of asbestos-related lung cancer are compensated, despite recent changes to the eligibility criteria.
Reports from the SWORD/OPRA surveillance scheme provide data on the number of cases of occupational Lung Cancer reported to chest physicians and occupational physicians, as shown in Table THORR01. The estimated number of cases of lung cancer, without specifying whether or not they were asbestos-related, has fluctuated somewhat erratically since 1998 with an average of 113 cases per year. Table THORS01 shows the number of cases of occupational skin cancer reported to occupational physicians and dermatologists in the EPIDERM/OPRA scheme. The estimated number of cases of skin cancer has also varied considerably, with an average 488 estimated cases per year. However, statistical modelling of the EPIDERM/OPRA data by the University of Manchester to allow for various factors that affect reporting levels (including the number and type of participating specialists and occupational physicians, their reporting habits, and seasonal effects) suggests an overall downward trend in incidence.
