- Mesothelioma incidence has increased over the last 25 years in Ontario, but it appears to have leveled off after 2010, driven by decreasing incidence among men.
- Mesothelioma rates among women have always been much lower than among men, but they are slowly rising.
- Cases are also being diagnosed at an older age. The rates among people over age 70 have risen dramatically, while there has been little or no change among people below age 50.
The number of mesothelioma cases in Ontario and the incidence rates per 100,000 people have been rising for decades due to a growing and aging population, but incidence rates for men and women have started to change. Mesothelioma is a cancer of the tissue that lines internal organs, including the lungs, digestive organs, heart and sex organs. It is caused by exposure to asbestos and similar naturally occurring mineral fibres.
In recent years, mesothelioma incidence rates appear to have leveled off overall, driven by changes in incidence among men. Although the rate in any year can rise and fall, the rates among men appear to be starting to decrease. Among women, mesothelioma incidence rates are much lower, but appear to be slowly increasing. In addition, the rates among men and women over age 70 have risen dramatically, while there has been little or no change among people below age 50 (data not shown).
The trends observed here in Ontario have been seen in other countries. The higher mesothelioma incidence rates among men reflect their much higher levels of occupational asbestos exposure in the past. Mesothelioma generally develops 30 to 40 years after first exposure and exposures in Canada began decreasing in the 1970s, so rates were expected to drop eventually. However, lower levels of exposure continue to occur, so mesothelioma will not disappear. Over time, more women may have occupational exposure due to changing employment patterns.
In addition, women and men may be exposed in their homes and communities, such as through poorly contained asbestos in residential buildings. These lower levels of exposure could lead to the development of mesothelioma later in life. More research is needed to understand the changing demographic patterns of mesothelioma.
Mesothelioma is a rare cancer with extremely poor survival, with a median survival time of less than 1 year. Approximately 80% to 85% of all mesothelioma cases are believed to be associated with occupational asbestos exposure.
Asbestos was historically used in many applications, including:
- insulation in buildings and ships
- fire-proofing textiles
- strengthening brake pads, cement pipe and gaskets
In 2018, the Government of Canada banned most uses of asbestos. However, mesothelioma will persist for many decades due to long latency periods and the continuing presence of asbestos in many products, such as older building materials.
In recent years, approximately 240 mesotheliomas were diagnosed annually in Ontario. Although overall rates may have leveled off, these numbers are unlikely to decrease soon. CAREX Canada estimates that approximately 50,000 people in Ontario continue to be occupationally exposed to asbestos. Most exposures take place among workers in the construction industry who maintain, renovate and demolish older buildings containing asbestos. These workers will be at risk for mesothelioma in the future. There is a continuing need to monitor mesothelioma trends to better understand changes related to latency, levels of exposure and environmental sources.
For more information about asbestos, its impact on Ontario and exposure prevention, please see: