Historically, the study of occupational cancers was started in 1775 by Sir Percivall Pott. He recognised that exposure to a chemical agent in the workplace could cause a specific malignancy. In particular, Pott observed an increased incidence of squamous cell carcinoma of the scrotum in “climbing boys”, which he attributed to soot (1). Now it is known that polycyclic aromatic hydrocarbons and particularly 3,4-benzpyrene were the chemicals causing scrotal cancer in the small boys, who assisted chimney sweeps (2). A century after Pott’s report, in 1895, Rehn noted an association between exposure to aromatic amines and bladder cancer among workers in the aniline dye industry (2).
Nowadays, the study of occupational cancers is an important field of research with unique potentials for prevention, which has expanded to an international level. But work-related malignancies still place a heavy psychological and financial burden on our society in terms of compensation, treatment costs and most importantly human suffering. It has been estimated that approximately 4% of all cancer deaths, in people above the age of 15, may have an occupational origin (3,4). This is probably an underestimation of the true health problem posed by work-related cancers. The main contributing factor to this underreporting is the lack of data on the tumourigenic potential of most industrial compounds (2,4). Thus, millions of workers, especially in small private businesses and in the informal sector, might be exposed to occupational carcinogens that have not yet been identified (2). Remember that these people can be our friends, colleagues, relatives or even ourselves!
What is an occupational carcinogen?
Any biological, chemical or physical agent or exposure circumstance in the workplace, which has the potential to cause malignancies in humans can be defined as an occupational carcinogen (3). Siemiatycki et al. identified that 168 out of all the agents classified as carcinogens are related to occupational exposures (5).
Why is it difficult to identify carcinogens?
Most of the evidence for the carcinogenic potential of a substance has been derived either from animal or epidemiological studies. Animal studies have the advantage of controlled environmental conditions, but the findings do not necessarily apply to humans. On the other hand, experiments on humans are not possible due to obvious ethical reasons. Thus, reliance is placed on epidemiological studies, in which unknown factors may exist and confound the analysis of the results (6). Another major difficulty in such studies is that work-related cancers are characterised by a long latency period between initial exposure and disease presentation (3).
Which are the most common occupational carcinogens and their cancer sites?
Several occupational carcinogens have been identified and a well-known example is asbestos. This includes a group of naturally occurring fibrous minerals, which are mainly used in thermal and acoustic insulation (6). It is commonly classified, dependent on its colour, as: blue (crocidolite); brown (amosite); and white (chrysotile). The main sources of exposure have occurred in: ship-building; railway engineering; the construction industry; and asbestos mining and milling (7).
Asbestos exposure is a recognised cause for lung cancer, mesothelioma of the pleura and rarely mesothelioma of the peritoneum (3,6). Mesothelioma of the pleura is a fatal malignancy and it has a median survival of approximately 12 months after the initial diagnosis (3). In the case of lung cancer, there is a synergistic effect between tobacco use and asbestos. Thus, smoking can make the causal relationship between this natural fibre and the malignancy less specific and therefore difficult to assess (7). Asbestos has also been linked to laryngeal and gastrointestinal cancers (7). However, these associations have not yet been firmly established and further research is required into this field of medicine.
Silica (silicon dioxide) is an inorganic particle occurring in two forms, amorphous and crystalline. IARC classified the latter as a definite carcinogen (Group 1) in 1997. The most abundant polymorph of crystalline is quartz, which is used in a wide range of industrial processes. The main sources of exposure include the ceramic industry; foundries; and sandblasting operations. Clapp et al. suggests that there is strong evidence associating crystalline silica with an increased risk of lung cancer (6).
Aromatic amines are organic compounds with a characteristic odour, several of which are potent urinary tract carcinogens. The metabolite formed in the liver, rather than the actual amine, is probably responsible for causing malignancies. The target organ is usually the bladder, but any part of the urothelial tract, which is compromised of transitional epithelium, can be affected (3).
Polycyclic aromatic hydrocarbons are formed by the incomplete combustion of organic material including coal, oil and petrol. Thus, the heaviest exposures occur in coke ovens; coal gas manufacture; aluminium production; and petroleum refineries. Inhalation of polycyclic aromatic hydrocarbons causes lung cancer and probably bladder cancer, whereas dermal exposure can lead to the development of squamous cell carcinoma (6,7).
Regarding metals and metal compounds arsenic, beryllium, cadmium, hexavalent chromium (VI) and selected nickel compounds have been classified as definite human carcinogens (Group 1) by the IARC (5). The main target organ is the lung, but other sites can be affected as well (Table 1).(3,5,7)
Nowadays, the study of occupational cancers is an important field of research with unique potentials for prevention, which has expanded to an international level. But work-related malignancies still place a heavy psychological and financial burden on our society in terms of compensation, treatment costs and most importantly human suffering. It has been estimated that approximately 4% of all cancer deaths, in people above the age of 15, may have an occupational origin (3,4). This is probably an underestimation of the true health problem posed by work-related cancers. The main contributing factor to this underreporting is the lack of data on the tumourigenic potential of most industrial compounds (2,4). Thus, millions of workers, especially in small private businesses and in the informal sector, might be exposed to occupational carcinogens that have not yet been identified (2). Remember that these people can be our friends, colleagues, relatives or even ourselves!
What is an occupational carcinogen?
Any biological, chemical or physical agent or exposure circumstance in the workplace, which has the potential to cause malignancies in humans can be defined as an occupational carcinogen (3). Siemiatycki et al. identified that 168 out of all the agents classified as carcinogens are related to occupational exposures (5).
Why is it difficult to identify carcinogens?
Most of the evidence for the carcinogenic potential of a substance has been derived either from animal or epidemiological studies. Animal studies have the advantage of controlled environmental conditions, but the findings do not necessarily apply to humans. On the other hand, experiments on humans are not possible due to obvious ethical reasons. Thus, reliance is placed on epidemiological studies, in which unknown factors may exist and confound the analysis of the results (6). Another major difficulty in such studies is that work-related cancers are characterised by a long latency period between initial exposure and disease presentation (3).
Which are the most common occupational carcinogens and their cancer sites?
Several occupational carcinogens have been identified and a well-known example is asbestos. This includes a group of naturally occurring fibrous minerals, which are mainly used in thermal and acoustic insulation (6). It is commonly classified, dependent on its colour, as: blue (crocidolite); brown (amosite); and white (chrysotile). The main sources of exposure have occurred in: ship-building; railway engineering; the construction industry; and asbestos mining and milling (7).
Asbestos exposure is a recognised cause for lung cancer, mesothelioma of the pleura and rarely mesothelioma of the peritoneum (3,6). Mesothelioma of the pleura is a fatal malignancy and it has a median survival of approximately 12 months after the initial diagnosis (3). In the case of lung cancer, there is a synergistic effect between tobacco use and asbestos. Thus, smoking can make the causal relationship between this natural fibre and the malignancy less specific and therefore difficult to assess (7). Asbestos has also been linked to laryngeal and gastrointestinal cancers (7). However, these associations have not yet been firmly established and further research is required into this field of medicine.
Silica (silicon dioxide) is an inorganic particle occurring in two forms, amorphous and crystalline. IARC classified the latter as a definite carcinogen (Group 1) in 1997. The most abundant polymorph of crystalline is quartz, which is used in a wide range of industrial processes. The main sources of exposure include the ceramic industry; foundries; and sandblasting operations. Clapp et al. suggests that there is strong evidence associating crystalline silica with an increased risk of lung cancer (6).
Aromatic amines are organic compounds with a characteristic odour, several of which are potent urinary tract carcinogens. The metabolite formed in the liver, rather than the actual amine, is probably responsible for causing malignancies. The target organ is usually the bladder, but any part of the urothelial tract, which is compromised of transitional epithelium, can be affected (3).
Polycyclic aromatic hydrocarbons are formed by the incomplete combustion of organic material including coal, oil and petrol. Thus, the heaviest exposures occur in coke ovens; coal gas manufacture; aluminium production; and petroleum refineries. Inhalation of polycyclic aromatic hydrocarbons causes lung cancer and probably bladder cancer, whereas dermal exposure can lead to the development of squamous cell carcinoma (6,7).
Regarding metals and metal compounds arsenic, beryllium, cadmium, hexavalent chromium (VI) and selected nickel compounds have been classified as definite human carcinogens (Group 1) by the IARC (5). The main target organ is the lung, but other sites can be affected as well (Table 1).(3,5,7)
