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
    • 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.

    • 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

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.

    • 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.

    • 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.

    • 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.