The current burden of cancer attributable to occupational exposures in Canada

Our plain-English summary of The current burden of cancer attributable to occupational exposures in Canada, by F. Labrèche, J. Kim, C. Song, et al (Preventive Medicine, 2019).

The study

• Authors: F. Labrèche, J. Kim, C. Song, M. Pahwa, C.B. Ge, V.H. Arrandale, C.B. McLeod, C.E. Peters, J. Lavoué, H.W. Davies, A.M. Nicol, P.A. Demers
• Journal: Preventive Medicine
• Published: 2019;122:128-139
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

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.

Copyright © 2019. Published by Elsevier Inc.

In plain English

This study estimated how many cancers diagnosed in Canada in 2011 were attributable to workplace carcinogens, combining exposure estimates from CAREX Canada, census and labour force data with relative risks taken mainly from published studies. Using a low and a high estimate for night shift work and breast cancer, the authors estimated that 3.9% (95% CI 3.1% to 8.1%) or 4.2% (95% CI 3.3% to 8.7%) of cancers were due to occupational exposure, counting solid tumors from age 25 and blood and lymphoid tumors from age 15. Because historical exposure data were limited, asbestos was handled differently. For mesothelioma, the authors applied proportions from French, British and American case-control studies: 85% of cases in men, and 60% in women counting para-occupational exposure, giving 427 of 530 cases. Asbestos was estimated to account for 8.01% of lung cancers (95% CI 4.92% to 13.05%), or 1904 cases (1168 to 3101): 13.76% (8.44% to 22.41%) in men and 1.58% (0.97% to 2.58%) in women. The authors stated that using an incomplete list of carcinogens almost certainly underestimated the total burden.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Burden-of-disease (population attributable risk) estimation study. Exposure prevalence was combined with published relative risks using Levin's equation.
• Who was studied: Canadians alive in 2011 who were of working age (15 to 65) at any point during the risk exposure period (1961 to 2001 for solid tumors). Estimates were applied to cancers diagnosed in 2011 and recorded in the Canadian Cancer Registry: solid tumors in people aged 25 and over, and blood and lymphoid tumors in people aged 15 and over.
• Exposure: 44 occupational carcinogens (IARC Group 1 or 2A) were initially selected, and PARs were estimated for 64 exposure-cancer pairs. Asbestos (fiber types not specified) was handled with a different method. For mesothelioma, attributable proportions of 85% in men and 60% in women (occupational and para-occupational) were taken from three case-control studies. For lung cancer, an excess lung cancer to mesothelioma ratio of 4.67 (95% CI 2.87 to 7.61) was taken from an unpublished meta-analysis.
• Main results:
  • Cancers diagnosed in Canada in 2011 (solid tumors at age 25 and over, blood and lymphoid tumors at age 15 and over): between 3.9% (95% CI 3.1% to 8.1%) and 4.2% (95% CI 3.3% to 8.7%) were estimated to be due to occupational exposure. The two estimates come from using a low and a high estimate for night shift work and breast cancer.
  • In numbers of cases, the minimum estimate was 7700 and the maximum was 21,800 attributable cases. These are the lower and upper confidence limits.
  • Mesothelioma: asbestos was estimated to be responsible for 80.6% of cases overall, 427 of 530 cases in 2011 (Table 2). In men the figure was 85%, 370 of 435 cases; in women it was 60%, 57 of 95 cases. These proportions were applied from other studies rather than measured in Canada.
  • Lung cancer (all Canadians, 23,735 cases in 2011): asbestos PAR was 8.01% (95% CI 4.92 to 13.05), or 1904 cases (1168 to 3101). In men it was 13.76% (8.44 to 22.41), or 1727 cases (1059 to 2812). In women it was 1.58% (0.97 to 2.58), or 177 cases (109 to 289).
  • Combined lung cancer PAR for 17 occupational lung carcinogens, including asbestos: 14.9% overall (about 3500 cases), 24.4% in men and 3.4% in women.
  • Other exposures with the most attributable cases were solar radiation (more than 4500 non-melanoma skin cancers) and night shift work among women (470 to 1200 breast cancers).
• The authors' conclusion: The authors concluded that their results highlight several occupational exposures and associated cancer sites that need recognition and preventive efforts. They added that further methodologic work is still warranted.
• Limitations the authors state:
  • The methodologic assumptions and limited exposure data may have produced both underestimates and overestimates of the true burden.
  • An incomplete list of occupational carcinogens was used, which almost certainly underestimated the overall burden.
  • The same latency period was assumed for all solid tumors. This affects the estimated number of exposed workers and therefore the PARs.
  • In some cases exposure levels had to be grouped into broad categories or simply exposed versus not exposed. This may have increased non-differential misclassification and uncertainty.
  • PAR estimation assumes a causal relationship, yet two of the included exposures were only probable carcinogens.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Population Attributable Fraction (PAF), Cancer Registry, Mesothelioma, Crystalline.

Related studies

• An estimate of cancers attributable to occupational exposures in France — P. Boffetta, P. Autier, et al. (2010)
• Cancers in France in 2015 attributable to occupational exposures — C. Marant Micallef, K.D. Shield, et al. (2019)
• The global burden of cancers attributable to occupational factors, 1990-2021 — B. Zou, P. Wu, et al. (2025)
• An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada — S.L. Greco, E. MacIntyre, et al. (2020)
• The future excess fraction of occupational cancer among those exposed to carcinogens at work in Australia in 2012 — R.N. Carey, S.J. Hutchings, et al. (2017)
• Occupational cancer burden in Great Britain — L. Rushton, S.J. Hutchings, et al. (2012)

Browse more research in Preventive Medicine, or return to medical research.