Choice of health outcomes

Work-related malignant conditions can arise from a variety of exposures, but we consider only the three  main documented occupational cancers: lung cancer, leukaemia and malignant mesothelioma.  Although other cancers are known to have occupational causes, there are not enough data on exposure and risk, and the number of cases are too few, for the data to be  included in this guide.  These other cancers
(and their causative agents) include:

1. bladder cancer (aromatic amines, benzidine dyes and methylene-bis-ortho-chloroaniline);
2. liver cancer (vinyl chloride);
3. nasal cavity and middle ear cancer (hardwood dust, chromium VI compounds, nickel compounds);
4. bone and articular cartilage cancer (ionizing radiation);
5. skin cancer (arsenic, by-products of distillation, ionizing radiation);
6. lung cancer (from passive smoke in the workplace).

In the comparative risk assessment (CRA) study of Concha-Barrientos et al. (2004), the criteria used to assess causal connections between exposures and outcomes of interest were a consistent relationship between the risk factor and the outcome across different studies and settings; and the strength of the evidence of the relationship.
Data sources were evaluated to assess the strength of the evidence linking specific cancers with exposure to chemical or physical agents.

The burden of disease from occupational exposures

Nurminen & Karjalainen (2001) estimated  the proportion of fatalities related to occupational factors in Finland.  The average number of exposed workers in Finland was estimated from census data stratified by gender, age, occupation and industry, and from the FINJEM national job-exposure matrix.  Relative risks were obtained from review of epidemiological studies, focusing on risk estimates that were most valid for the Finnish exposure circumstances.  

The authors used AF methodology to determine the proportion of deaths in  the population attributable to occupational factors, and reported that 30% of these deaths in 1996 were caused by cancer.  Occupational lung cancer accounted for 0.9% of all deaths, and leukaemia, malignant mesothelioma and other cancers together accounted for another 0.2% of all deaths.The authors attributed 24% of bronchus and lung cancers (29% for men and 5.3% for women) to occupational exposures to combined risk factors. 

The AFs for urinary cancer were 10.3% overall, and 14.2% for men and 0.7%  for women.  Occupational risk factors also accounted for 10.9% (18.5% for males, 2.5% for females) of leukaemia deaths, the majority (17.8% for males and 2.3% for females) from electrical occupations.  In contrast, only 0.7% (males) and 0.2% (females) of leukaemia deaths were attributable to occupational exposure to benzene.  For malignant mesothelioma cases, an average of 71.3% (90% for males, 25% for females) was attributed to occupation.

Identification of the risk factors

The International Agency for Research  on Cancer (IARC, 2002) has classified 150 chemical or biological agents as known or probable human carcinogens, and exposures to many of these carcinogens (e.g. asbestos, cadmium and benzene) occur in occupational settings.  Occupational exposure is defined as any contact between the human body and a potentially harmful agent or environment in the workplace.
Specific exposures are related to the type  of work that people do (i.e. occupation), where they do it (e.g. the industrial sector − also called the economic sector) and the measures that are taken to limit exposures.  The probability that a worker will develop cancer is influenced by the total dose of carcinogen received, the potency of the carcinogen, the presence of other exposures (notably tobacco smoking), and individual susceptibility.  Excess exposure to carcinogens can lead to changes at the cellular level, resulting in  the uncontrolled growth of abnormal cells that invade and destroy normal tissues in the lung, blood system, etc.  

IARC has classified 87 agents, mixtures, or exposure circumstances as Group 1 Carcinogenic to Humans, including various chemical compounds, pharmaceuticals, and bacterial and viral infections.  An additional 63 agents, mixtures, or exposure  circumstances have been classified as Group 2A Probably Carcinogenic to Humans (IARC, 2001).  

With the exceptions described below, the analysis in this document includes IARC Group 1 and 2A carcinogens associated with cancers  of the lung, leukaemia, and malignant mesothelioma.
The most important lung carcinogens in occupational settings are asbestos, radon, arsenic, chromium, silica, beryllium, nickel, cadmium and diesel exhaust.  The most important agents for leukaemia are benzene, ionizing radiation and ethylene oxide.
Asbestos is a causal agent of asbestosis, lung cancer and malignant mesothelioma, and silica causes silicosis in addition to lung cancer (the role of asbestos in asbestosis and silica in silicosis is also considered in a forthcoming guide in the EBD series, on occupational airborne particulates). 

Magnitude, Rates , Sex, Race, Occupation

Magnitude and Trend

Number of U.S. residents aged 15 or older with malignant mesothelioma listed as an underlying or contributing cause on the death certificate by type of mesothelioma, 1999. Of the 2,485 malignant mesothelioma deaths in 1999, the highest proportion was classified as an unspecified type. In nearly 95% of all deaths, malignant mesothelioma was listed as the underlying cause. (Note: The total number of deaths by subtype exceeds the number for all sites because more than one subtype was listed for some decedents.)

Rates among States

Age-adjusted mortality rates for malignant mesothelioma in U.S. residents aged 15 or older by State, 1999. The highest malignant mesothelioma mortality rates occurred in Alaska and Maine in 1999. The rates for each of these States were more than twice the national rate of 11.7 per million. States in the next highest rate group were widely dispersed, with a concentration on the eastern seaboard and in the West. The rates in these States were nearly 1.5 to 2 times the U.S. rate.

Sex and Race

Distribution and number of malignant mesothelioma deaths in U.S. residents aged 15 and older by sex and race, 1999. More than 80% of malignant mesothelioma deaths occurred in men in 1999. White residents accounted for 94.8% of malignant mesothelioma deaths.

Occupation and Industry

PMRs and 95% confidence intervals for malignant mesothelioma in U.S. residents aged 15 or older by industry and occupation, 1999. Industrial and miscellaneous chemicals, electric light and power, and construction industries were associated with the highest significant malignant mesothelioma PMRs. Plumbers, pipefitters, steamfitters, and electricians (which are occupations associated with the construction industry) were highly associated with malignant mesothelioma mortality. Elementary school teachers also had a significant malignant mesothelioma PMR. (Note: This figure presents the highest significant PMRs based on 10 or more deaths.)

Mesothelioma from Asbestos

Mesothelioma is a rare and deadly form of cancer that manifests itself years after the inhalation of airborne asbestos fibers.
It is known the world over as the signature asbestos-caused cancer. Three thousand cases of mesothelioma are diagnosed in America every year, according to the National Cancer Institute.
Many public figures have died from the ravages of one of the most deadly, yet preventable, cancers on record. Screen actor Steve McQueen and songwriter Warren Zevon, both of whom worked in asbestos-related occupations prior to their public careers, died of mesothelioma within months of being diagnosed.
In layman’s terms, the tissues that line our internal organs, including the lungs, are called “mesothelium.” Mesothelioma is cancer of that tissue. Some patients have been known to live longer, though most succumb to the disease within four to 14 months after being diagnosed. There is no known cure for mesothelioma, and treatment for this disease has not advanced far since the 1980s.
American auto plants are also notorious for exposing factory workers to asbestos, an ingredient still utilized to this day in automobile brake shoe linings. Since mesothelioma can take decades to develop (up to 50 years in some cases), these workers are only now being diagnosed.
Mesothelioma is usually caused by workplace exposure to airborne asbestos fibers. It is a preventable disease that is frequently the result of an employer’s choice for greater profits over worker health safety.