- Mesothelioma is a highly fatal cancer caused by exposure to asbestos.
- The number of new cases of mesothelioma diagnosed each year in Ontario is rising.
- The number of cases is expected to decline in the future due to decreased use of asbestos in Ontario.
Between 1981 and 2012, the number of newly diagnosed cases of mesothelioma among Ontario men rose steadily at an average of 5.5% per year, from about 30 cases in 1981 to about 180 in 2012. Incidence rates rose from 0.81 per 100,000 to 2.23 per 100,000 over the same period. Ontario’s incidence rate for mesothelioma was lower than the national average over the 1981–2012 period, but because Ontario’s population is large, the number of cases diagnosed each year was high in comparison to most other provinces.
Mesothelioma is a rare but highly fatal cancer. It affects the protective linings covering many of the body’s internal organs, most commonly the pleura, which cover the lungs. Almost all mesothelioma is caused by exposure to asbestos, the commercial term for a group of 6 naturally occurring mineral fibres. Asbestos has been used for many commercial applications, including insulation, textiles, roofing, brake pads and cement pipe. Approximately 85% of mesothelioma cases in men and 40% of cases in women are attributable to work-related asbestos exposure,   while most of the remainder are caused by other environmental asbestos exposure, such as exposure to asbestos-containing insulation in the home, or family members’ exposure to trace asbestos on workers’ clothing. Asbestos also causes lung, ovarian and laryngeal cancer, as well as asbestosis (scarring of the lungs). Mesothelioma rates in Ontario are highest in Lambton County due to heavy historic use of asbestos in Sarnia’s Chemical Valley.
Use of asbestos peaked in the 1960s and 1970s, and has declined significantly since then due to regulations and restrictions in use because of the adverse health effects. However, because mesothelioma takes a long time to develop, the current burden of disease is associated with asbestos exposure that occurred 10 to 50 years ago. The number of new cases of mesothelioma is expected to plateau and decline based on the pattern of decreased asbestos use, but it is difficult to predict when this will happen. Currently, new uses of asbestos in Canada are limited to friction products, cement and a small number of other specialized products. Most exposure today occurs when asbestos-containing materials in older buildings or other products deteriorate or are disturbed during maintenance, repair, or remediation. CAREX Canada, a national carcinogen surveillance program, has estimated that approximately 52,000 Ontarians are still exposed to asbestos in the workplace, most in the construction, automotive repair, remediation and ship building industries. Asbestos exposure today will impact the future burden of asbestos-related disease.