Mesothelioma
Background
What is mesothelioma?
Mesothelioma is a cancer of the tissue lining the lungs and other organs caused by exposure to inhaled asbestos fibres. It is characterized by a long latency period: the onset of disease can be as much as 50 years after exposure to asbestos fibres. There is no cure and survival is extremely poor.
Risk factors
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- Asbestos fibres (all types)
- Asbestos-like fibres (erionite and fluoro-edenite)
Asbestos is the commercial name for a group of naturally occurring mineral fibres. It was historically used in many commercial applications including insulation, roofing, cement pipe and sheets, gaskets, and friction materials. Use of asbestos was banned in Canada in 2018, although it is still found in many older products and buildings. The Burden of Occupational Cancer in Canada Study estimates that approximately 80% of mesothelioma cases are attributable to occupational asbestos exposure.
Key Findings
The greatest risks of mesothelioma were observed among workers employed in the construction, education, mining, and manufacturing sectors.
Construction
Workers in the construction industry are at an increased risk of mesothelioma. Within the construction industry, insulators and pipefitters and plumbers have the highest risk, but many other trades are also at increased risks of mesothelioma. Insulating occupations historically required workers to handle asbestos-containing materials when installing or removing insulation materials from homes. Many construction trades may still be exposed to asbestos during renovation, maintenance or demolition of buildings built prior to 1980.
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- All construction trades occupations: 2.4 times the risk
- Insulators: 27 times the risk
- Pipefitters and plumbers: 6 times the risk
- Electricians and repairmen: 2.2 times the risk
- Carpenters: 1.8 times the risk
- All construction trades occupations: 2.4 times the risk
Education and Related Services
Workers within the education and related services sector include not only teachers and administrative staff, but also custodial workers. Asbestos-containing materials, such as pipe insulation, may be found in older schools and buildings. As asbestos-containing materials degrade, fibres can become airborne and pose a health risk to staff. Custodial workers especially are at risk of exposure during building maintenance and repair. ODSS results indicate that university and college staff as well as elementary and secondary school staff are at increased risks of mesothelioma, but specific subgroups, such as custodial workers, are likely driving these observed findings.
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- Universities and colleges: 2.8 times the risk
- Elementary and secondary schools: 1.6 times the risk
Mining
Unlike Quebec, Ontario’s asbestos mining was a small industry. The majority of production occurred between 1950 and 1978. Nevertheless, ODSS results demonstrate that asbestos miners in Ontario are at a dramatically increased risk of mesothelioma. This is an expected finding given the extraordinarily high levels of exposure likely to have occurred among asbestos miners.
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- Asbestos miners: 260 times the risk
Metal Manufacturing
Asbestos was commonly used as an insulating material in metalworking machinery. Within the metal manufacturing industry, workers may operate and repair boilers, furnaces, and other heating apparatuses insulated with asbestos. The ODSS detected that iron and steel workers and boilermakers, platers, and structural metal workers are at increased risks of mesothelioma.
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- Iron and steel workers: 1.8 times the risk
- Boilermakers, platers, and structural metal workers: 4.5 times the risk
Relative Risk by Industry and Occupation
Figure 1. Risk of mesothelioma diagnosis among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).
Figure 2. Risk of mesothelioma diagnosis among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).
Table of Results
Table 1. Surveillance of Mesothelioma: Number of cases, workers employed, and hazard ratios in each industry (SIC)
SIC Code * | Industry Group | Number of cases | Number of workers employed | Hazard Ratio (95% CI) † |
1 | Agriculture | 11 | 35,119 | 0.90 (0.50, 1.64) |
2/3 | Forestry, Fishing and Trapping | <5 | 10,722 | — |
4 | Mines, Quarries and Oil Wells | 21 | 23,230 | 1.22 (0.79, 1.89) |
5 | Manufacturing | 340 | 694,923 | 1.06 (0.92, 1.22) |
6 | Construction | 170 | 211,572 | 1.89 (1.60, 2.24) |
7 | Transportation, Communication and Other Utilities | 83 | 197,583 | 0.94 (0.75, 1.19) |
8 | Trade | 93 | 429,967 | 0.71 (0.57, 0.88) |
9 | Finance, Insurance and Real Estate | 6 | 24,021 | 0.61 (0.27, 1.37) |
10 | Community, Business and Personal Service | 126 | 600,449 | 0.98 (0.80, 1.19) |
11 | Public Administration and Defense | 82 | 191,139 | 1.06 (0.84, 1.33) |
* SIC: Standard Industrial Classification (1970) | ||||
† Hazard ratio in each group relative to all others |
Table 2. Surveillance of Mesothelioma: Number of cases, workers employed, and hazard ratios in each occupation (CCDO) group
CCDO Code * | Occupation Group | Number of cases | Number of workers employed | Hazard Ratio (95% CI) † |
11 | Managerial, administrative and related | 15 | 31,037 | 2.14 (1.29, 3.57) |
21 | Natural sciences, engineering and mathematics | 12 | 26,369 | 1.35 (0.76, 2.38) |
23 | Social sciences and related fields | <5 | 30,728 | — |
25 | Religion | 0 | 129 | — |
27 | Teaching and related | 9 | 48,524 | 1.30 (0.67, 2.51) |
31 | Medicine and health | 17 | 135,476 | 1.03 (0.62, 1.70) |
33 | Artistic, literary, recreational and related | <5 | 15,009 | — |
41 | Clerical and related | 35 | 197,593 | 0.69 (0.49, 0.97) |
51 | Sales | 20 | 148,272 | 0.77 (0.49, 1.20) |
61 | Service | 77 | 371,368 | 0.74 (0.58, 0.94) |
71 | Farming, horticultural and animal husbandry | 12 | 50,269 | 0.71 (0.40, 1.25) |
73 | Fishing, hunting, trapping and related | 0 | 558 | — |
75 | Forestry and logging | <5 | 10,710 | — |
77 | Mining and quarrying, including oil and gas field | 7 | 13,046 | 0.75 (0.36, 1.59) |
81 | Processing (mineral, metal, chemical) | 33 | 79,386 | 1.05 (0.74, 1.48) |
82 | Processing (food, wood, textile) | 19 | 99,382 | 0.56 (0.35, 0.88) |
83 | Machining and related | 109 | 189,800 | 1.21 (0.99, 1.48) |
85 | Product fabricating, assembling and repairing | 157 | 328,825 | 1.08 (0.91, 1.29) |
87 | Construction trades | 223 | 216,117 | 2.39 (2.04, 2.79) |
91 | Transport equipment operating | 54 | 168,487 | 0.65 (0.49, 0.86) |
93 | Materials handling and related, not elsewhere classified | 55 | 153,323 | 0.96 (0.73, 1.26) |
95 | Other crafts and equipment operating | 20 | 28,360 | 1.56 (1.00, 2.43) |
99 | Other occupations not elsewhere classified | 85 | 215,629 | 1.03 (0.82, 1.29) |
* CCDO: Canadian Classification Dictionary of Occupations (1971) | ||||
† Hazard ratio in each group relative to all others |
Please note that ODSS results shown here may differ from those previously published or presented. This may occur due to changes in case definitions, methodological approaches, and the ongoing nature of the surveillance cohort.