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

Time Trends

Figure 1. Crude incidence rate of mesothelioma among males in the ODSS, 1985-2014 (n=2.18 million)

The crude incidence rate is the number of cases of disease diagnosed per person per year of follow-up in the ODSS cohort. The age-standardized incidence rate is the rate we would observe if we removed the influence of aging in the cohort over time. The general population of males in Ontario in 1995 was used as the standard. All rates are expressed per 100,000 persons per year.

Figure 2. Age-standardized incidence rate of mesothelioma among males in the ODSS, 1995-2014 (n=2.18 million)

The crude incidence rate is the number of cases of disease diagnosed per person per year of follow-up in the ODSS cohort. The age-standardized incidence rate is the rate we would observe if we removed the influence of aging in the cohort over time. The general population of males in Ontario in 1995 was used as the standard. All rates are expressed per 100,000 persons per year.