Risk Factors | Cancer Prevention Institute of Canada

Occupationally-related cancers make up a small fraction of all cancers, but the prevalence increases greatly when the population is restricted to those directly at risk. For example, an estimated 9% of men in occupations characterized by

carcinogen exposure contract lung cancer.[1] One study suggested that 13 to 18% of lung cancers in European men may be attributable to occupational carcinogens.[2] Overall, it is estimated that 9% of all malignancies in men can be traced to the workplace.[3]

Occupational exposure has always figured highly in cancer studies. Apart from final conclusions on prevalence and risk levels, there are several motivations for identifying carcinogens in the workplace:[4]

Categorizing Carcinogens

There are many complexities with identifying occupational carcinogens. Most occupational exposures are also found in the environment, including consumer products. For example, though asbestos, benzene and radon gas are considered occupational hazards, “it is likely that many more people are exposed to these substances outside than inside the occupational environment.”[9] Most environmental agents and consumer products are found in some occupational settings. This includes, naturally, substances in air and water, but also medications, foods and others. As well, sunlight can be a cancer risk factor in outdoor work (see the previous section of this report). The distinction between occupational and environmental carcinogens can thus be quite arbitrary.

Occupational Carcinogens

Only about 2% of the 50,000 chemicals used in industry have been evaluated for carcinogenicity.[10] It is clear that many more hazardous agents may be discovered, though for now there has been “a shift away from occupational cancer research in the epidemiologic community.”[11] One reason for the reduced emphasis is the decreased exposure to some recognized carcinogens; in other words, there have been some public and occupational health success stories, e.g., modifications in the dyestuff industry which has reduced bladder cancer rates. However, the rise of new industries with unassessed risks, and the “export” of high risk industries to developing countries, means that the prevention task is hardly complete.[12]

The International Agency for Research on Cancer (IARC)[13] classifies the evidence identifying a carcinogen as sufficient, limited or inadequate; there also may be definite evidence for a lack of carcinogenicity (in 1996, only 1 chemical out of 782 examined agents fit this last category).[14] Sufficient evidence means that the data points to actual causation, i.e., the substance causes cancer. The second category, limited evidence, is sometimes divided into probably and possibly carcinogenic.

The growth in the number of known carcinogens identified by the IARC can be seen in the following table:[15]

Category	1972-1995	1972-2004
Carcinogenic Substances	66	95
Probably Carcinogenic	51	66
*Total*	117	161

One of the most recent substances added to the list was environmental tobacco smoke (May, 2004). As a comparison, the US National Toxicity Program identified 228 carcinogens (52 definite)[16] in its biennial report of December, 2002. Of course, not all carcinogens on the list are chemicals, e.g., ultraviolet (see the previous major section of this report) and other types of radiation.[17] In fact, one of the prototype carcinogenic agents was x-rays, which, ironically, first came to light in healthcare settings.[18]

Narrowing the total number of hazards down to specifically occupational carcinogens is a difficult task, for reasons noted above. A November, 2004, report involving Canadian researchers summarized the best current understanding, based on IARC data, as follows:

Thus only a third of the entire list of definite / probable carcinogens has been associated significantly with workplaces. As a further comparison, the US National Institute for Occupational Safety and Health has 133 agents on its 2004 list of occupational carcinogens; their criteria and methods of selection are not clear.[19]

Occupational carcinogens can be further analyzed according to the precise occupations implicated and their target sites of cancer. Occupations with known exposure risks include:[20]

Known exposure risks - Aluminium production, boot and shoe manufacturing, coke production, cabinet making, iron and steel founding, painting, rubber industry.

Probable exposure risks - Art glass, hairdresser, insecticide use, petroleum refining.

Such identification of high-risk occupations needs to be qualified, as conditions can vary widely over different sites and over time. Likewise, a known carcinogen can have a variety of effects in different people under different circumstances; genetic factors, for instance, are known to play a role.[21],[22]

In terms of cancer sites, there is strong evidence of occupational carcinogenesis in nasal cavities, larynx, lung, liver, skin, bladder, thyroid and blood (specifically leukemia).[23] The lung is the target organ most affected by occupational carcinogens.

Prevention

This report will only examine prevention in reference to occupational carcinogens in general terms. Although a specific story could be told about each of the 50 to 150 known or probable cancer-causing hazards in workplaces (similar to

the presentation on environmental tobacco smoke earlier in this report), neither time nor space allows such an approach. What is most vital for the present report is to realize that the strategic framework for response is quite similar for many different carcinogens and occupations.

There are several precursors to an intervention in occupational settings, each of which represent a considerable challenge:

Control strategies for occupational carcinogens take place at two levels: societal and individual workplaces.

Societal Interventions

The response of a whole society or community to an occupational hazard involves various regulatory controls of decreasing intensity:[26],[27]

The surveillance systems mentioned in this list, while technically not a preventive measure, have proven to be invaluable in researching hazards, evaluating intervention effectiveness, and prompting necessary improvements in regulatory controls.[28] An example of a surveillance system in Canada is the National Dose Registry, which monitors exposure to ionizing radiation in a number of occupations. The risk assessment and surveillance task can be very complex when dealing with a mixture of agents in a workplace.[29] Synthesized rating and prioritizing methods have been proposed by some researchers.[30]

The outright ban of an industrial substance or process is quite rare. Even in more “intervention-friendly” Europe, bans and restrictions are still imposed very cautiously.[31] In 1967, 4 substances in addition to asbestos were banned in the UK; by 2004, no materials had been added to this list anywhere in Europe.[32]

By far the most common active intervention related to occupational carcinogens is regulated exposure levels, with or without a surveillance system. The occupational exposure limits (also known as threshold limit values or permissible exposure limits), which should be reviewed upon the development of new evidence,[33] serve to set the standards which are intended to minimize risk to workers. The rule of thumb is to limit risk to no more than 1 case per million over a lifetime.[34]

“Right to know” and other educational policies exist in many jurisdictions. In Canada, the Workplace Hazardous Materials Information System requires disclosure to workers handling hazardous products. The main communication tool is the Material Safety Data Sheet, which lists ingredients in a product that are considered to be toxic; carcinogens are noted if they compose more than 0.1% of the product.[35] Methods to improve these means of informing workers are being investigated.[36] The ultimate aim is to equip workers to be able to care for their own welfare.

A parallel to informing workers is the labelling of manufactured goods to reveal whether or not they are free of hazardous chemicals. This “eco-labelling” approach, more widespread in Europe than in Canada or the US, serves to create some pressure on companies to modify their industrial processes.

Although most of the preceding interventions are of a policy nature, many other community-based actions are also undertaken throughout Canada, aimed at educating the public, creating coalitions, and launching various forms of advocacy directed at government and / or industry. In the field of occupational health, some of the strongest and most influential action has come from unions. [37] When the focus is carcinogens, organizations such as the Canadian Cancer Society are playing an increasing role in developing preventive strategies.

There is undoubtedly much more work to be done in Canada and the various provinces regarding occupational carcinogens. One telling sign is the fact that the Canadian Environmental Protection Act (1999) does not target carcinogens. A recent scan of Canadian initiatives in this area concluded: “there is no focus on carcinogens as chemicals of high concern, as there is in Europe, and there is no articulated policy or strategy for reducing or eliminating them.”[38]

Workplace-based Interventions

Whether mandated by government or adopted voluntarily, various interventions are available in the workplace in order to eliminate or reduce carcinogen exposure. A well-accepted principle in managing occupational hazards involves a so-called “hierarchy of controls,” beginning with a first line of defence, near the hazard source, and leading to the last measure to be employed, near the worker. The comprehensive US report Preventing Illness and Injury in the Workplace provides a convenient summary of the possible interventions:[39]

Clinical Care

Clinicians treating people with cancer should take a history that reveals any occupational risks. One of the main motivations for identifying the potential involvement of a carcinogen is the possibility of alerting employers and other employees of the presence of the risk in the workplace (i.e., primary prevention). It is salient to note that “virtually all occupational carcinogens have first been recognized by astute clinicians.”[40]

Secondary prevention is also a goal where a full illness has not yet manifested. In particular, it is vital to counsel the affected patient to avoid exposure to co-carcinogens that can exacerbate their condition.[41] These agents are either environmental triggers working opportunistically, e.g., viruses, or modifiable behavioural risk factors. The best known example of the latter type of synergistic risk is that of lung cancer in asbestos workers who also smoke, which is more than 50 times the risk in non-smoking asbestos workers.[42]

[1] Morabia A, Markowitz S, Garibaldi K et al. Lung cancer and occupation: results of a multicentre case-control study British Journal of Industrial Medicine 1992; 49(10): 721-7.

[2] Boffetta P, Kogevinas M. Introduction: epidemiologic research and prevention of occupational cancer in Europe Environmental Health Perspectives 1999; 107(Suppl 2): 229-31.

[3] Miller AB. The information explosion: the role of the epidemiologist Cancer Forum 1984; 8: 67-75.

[4] Stellman JM, Stellman SD. Cancer and the workplace Ca: a Cancer Journal for Clinicians 1996; 46(2): 70-92.

[5] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[6] Blair A, Rothman N, Zahm SH. Occupational cancer epidemiology in the coming decades Scandinavian Journal of Work, Environment & Health 1999; 25(6): 491-7.

[7] Ward EM, Schulte PA, Bayard S et al. Priorities for development of research methods in occupational cancer Environmental Health Perspectives 2003; 111(1): 1-12.

[8] Lamontagne AD, Christiani DC. Prevention of work-related cancers New Solutions 2002; 12(2): 137-56.

[9] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[10] Stellman JM, Stellman SD. Cancer and the workplace Ca: a Cancer Journal for Clinicians 1996; 46(2): 70-92.

[11] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[12] Boffetta P, Kogevinas M. Introduction: Epidemiologic research and prevention of occupational cancer in Europe Environmental Health Perspectives 1999; 107(Suppl 2): 229-31.

[13] Goldsmith DF. Linking environmental cancer with occupational epidemiology research: the role of the International Agency for Research on Cancer (IARC) Journal of Environmental Pathology, Toxicology & Oncology 2000; 19(1-2): 171-5.

[14] Stellman JM, Stellman SD. Cancer and the workplace Ca: a Cancer Journal for Clinicians 1996; 46(2): 70-92.

[17] Wakeford R. The cancer epidemiology of radiation Oncogene 2004; 23: 6404-28.

[18] Stellman JM, Stellman SD. Cancer and the workplace Ca: a Cancer Journal for Clinicians 1996; 46(2): 70-92.

[19] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[20] Stellman JM, Stellman SD. Cancer and the workplace Ca: a Cancer Journal for Clinicians 1996; 46(2): 70-92.

[21] Thier R, Golka K, Bruning T et al. Genetic susceptibility to environmental toxicants: the interface between human and experimental studies in the development of new toxicological concepts Toxicology Letters 2002; 127(1-3): 321-7.

[22] Ishibe N, Kelsey KT. Genetic susceptibility to environmental and occupational cancers Cancer Causes & Control 1997; 8(3): 504-13.

[23] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[24] Siemiatycki J, Richardson L, Straif K et al. Listing of occupational carcinogens Environmental Health Perspectives 2004; 112(15): 1447-59.

[25] Verma DK, Purdham JT, Roels HA. Translating evidence about occupational conditions into strategies for prevention Occupational & Environmental Medicine 2002; 59(3): 205-13.

[26] Canadian Strategy for Cancer Control. Best Practices Review: Primary Prevention of Exposures to Occupational and Environmental Carcinogens. October, 2004.

[27] Verma DK, Purdham JT, Roels HA. Translating evidence about occupational conditions into strategies for prevention Occupational & Environmental Medicine 2002; 59(3): 205-13.

[28] Greife A, Halperin W, Groce D et al. Hazard surveillance: its role in primary prevention of occupational disease and injury Applied Occupational and Environmental Hygiene 1995; 10(9): 737-42.

[29] Tomatis L, Huff J, Hertz-Picciotto I et al. Avoided and avoidable risks of cancer Carcinogenesis 1997; 18(1): 97-105.

[30] LaMontagne AD, Youngstrom RA, Lewiton M et al. An exposure prevention rating method for intervention needs assessment and effectiveness evaluation. [Clinical Trial. Journal Article. Randomized Controlled Trial] Applied Occupational & Environmental Hygiene 18(7):523-34, 2003.

[31] Canadian Strategy for Cancer Control. Best Practices Review: Primary Prevention of Exposures to Occupational and Environmental Carcinogens. October, 2004.

[32] International Union Against Cancer. Evidence-based Cancer Prevention: Strategies for NGOs - A UICC Handbook for Europe. Available at http://www.uicc.org/index.php?id=976 (accessed December 2004).

[34] American Cancer Society. Available at http://www.cancer.org/docroot/PED/content/PED_1_3X_ Risk_Assessment.asp?sitearea=PED (accessed December 2004).

[35] Canadian Strategy for Cancer Control. Best Practices Review: Primary Prevention of Exposures to Occupational and Environmental Carcinogens. October, 2004.

[36] Niewohner J, Cox P, Gerrard S et al. Evaluating the efficacy of a mental models approach for improving occupational chemical risk protection Risk Analysis 2004; 24(2): 349-61.

[37] Canadian Strategy for Cancer Control. Best Practices Review: Primary Prevention of Exposures to Occupational and Environmental Carcinogens. October, 2004.

[38] Canadian Strategy for Cancer Control. Best Practices Review: Primary Prevention of Exposures to Occupational and Environmental Carcinogens. October, 2004.

[39] Preventing Illness and Injury in the Workplace. Washington, DC: U.S. Congress, Office of Technology Assessment, 1985.

[40] Landrigan PJ. The prevention of occupational cancer Ca: a Cancer Journal for Clinicians 1996; 46(2): 679.

[41] Haverkos HW. Viruses, chemicals and co-carcinogenesis Oncogene 2004; 23: 6492-99.

[42] Stellman SD. Interactions between smoking and other exposures: occupation and diet. In: Hoffmann D, Harris C (eds). Banbury Report No. 23, Mechanisms in Tobacco Carcinogenesis. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 1986.