Cancer is a complex group of diseases, each with many possible genetic, lifestyle and environmental causes. Chemicals, substances, and occupations are collectively referred to as exposures. Exposures that are known or suspected to cause cancer (carcinogens) are reviewed regularly by the International Agency for Research in Cancer (IARC). This agency follows a systematic process of assessing the world-wide body of research that has been done around an exposure to determine whether it can be officially classified as a known, probable or possible carcinogen.
Complete information about the classification system and the exposure reviews are available on the IARC website. Because this resource is not written for a lay audience, we’ve summarized some key information:
- Currently, there are 113 exposures classified as “known carcinogens”. These are exposures that have been proven, through many studies, to cause cancer in humans. Many of these substances have been banned in Canada, but others remain all around us, such as tobacco, alcohol, viruses, and ultraviolet radiation (sunlight). Polychlorinated biphenyls (PCB) were recently added to this list, in part due to research conducted in British Columbia.
- Exposures are classified as “probable carcinogens” when they have been shown to cause cancer in animals, but the evidence is less clear for humans. A recently-added example of a probable carcinogen is long-term shift work, which chronically disrupts the body’s normal sleep-wake cycles.
- Exposures that are termed “possible carcinogens” are those where currently there is only limited or inconsistent evidence in humans and insufficient evidence in animals. Much more research needs to be done to get a definitive answer. These include radiofrequency electro-magnetic fields (such as from mobile phones).
There is still a lot we don’t know about the causes of cancer. Plus, there are new chemicals and exposures being introduced into the environment every year. Long-term cohorts like the BC Generations Project provide our best chance to clarify whether current exposures are cancer causing. They also allow us to evaluate in the fastest possible way whether new exposures may be putting our health at risk.