The current burden of cancer attributable to occupational exposures in Canada

Highlights

• Proportion and number of cancers attributable to work inform effective prevention.

• In 2011, 9700–10,400 new cancer cases (3.9–4.2% of total) were attributable to work.

• Solar radiation, asbestos, silica, and diesel exhaust are major causes of occupational cancer.

• Most occupational cancers affect the skin, lung, breast, bladder or mesothelium.

Abstract

Exposure to occupational carcinogens is often overlooked as a contributor to the burden of cancer. To estimate the proportion of cancer cases attributable to occupational exposure in Canada in 2011, exposure prevalence and levels of 44 carcinogens were informed by data from the Canadian carcinogen exposure surveillance project (CAREX Canada). These were used with Canadian Census (between 1961 and 2011) and Labour Force Survey (annual surveys between 1976 and 2013) data to estimate the number of workers ever exposed to occupational carcinogens. Risk estimates of the association between each carcinogen and cancer site were selected mainly from published literature reviews. Population attributable risks were estimated using Levin's equation and applied to the 2011 cancer statistics from the Canadian Cancer Registry. It is estimated that 15.5 million Canadians alive in 2011 were exposed, during at least one year between 1961 and 2001, to at least one carcinogen in the workplace. Overall, we estimated that in 2011, between 3.9% (95% CI: 3.1%–8.1%) and 4.2% (95% CI: 3.3%–8.7%) of all incident cases of cancer were due to occupational exposure, corresponding to lower and upper numbers of 7700–21,800 cases. Five of the cancer sites – mesothelioma, non-melanoma skin cancer, lung, female breast, and urinary bladder – account for a total of 7600 to 21,200 cancers attributable to occupational exposures such as solar radiation, asbestos, diesel engine exhaust, crystalline silica, and night shift work. Our study highlights cancer sites and occupational exposures that need recognition and efforts by all stakeholders to avoid preventable cancers in the future.

Introduction

While numerous carcinogens have been discovered through the study of exposures of working populations (Loomis et al., 2018), only a few attempts have been undertaken to quantify the contribution of occupational exposures to the burden of cancer (Purdue et al., 2015). Doll and Peto (1981) estimated that 4% of all cancer deaths in the United States were attributable to occupational exposures, mentioning that this estimate was unlikely to be off by more than a factor of two. More recent estimates indeed varied between 2.4% and 8.4% (Boffetta et al., 2010; Dreyer et al., 1997; Nurminen and Karjalainen, 2001; Rushton et al., 2012; Steenland et al., 2003). Some of these studies were restricted to a small number of relatively high-burden carcinogens and few associated cancer sites, such as the Driscoll et al. (2005) study based on the Global Burden of Disease project. Other studies have considered close to ten cancer sites related to definite or probable carcinogens (Boffetta et al., 2010; Dreyer et al., 1997; Steenland et al., 2003). Only two studies estimated population attributable risks (PARs) for >20 cancer sites and attempted to provide more comprehensive estimates of the burden of cancer from occupational carcinogens. In Finland, Nurminen and Karjalainen (2001) estimated that, overall, 8.4% of cancer deaths (13.8% in men and 2.2% in women) were attributable to occupational exposure to definite and suspected carcinogens. A decade later, Rushton et al. (2012) estimated that 5.3% of cancer deaths (8.2% in men and 2.3% in women) were attributable to work-related exposure to known or probable carcinogens in Great Britain.

The objective of our current work, the Canadian Burden of Occupational Cancer study, was to estimate the number and proportion of cancer cases that were attributable, in 2011, to occupational exposure to carcinogens in Canada.