Cancer Risks among Welders and Occasional Welders in a National Population-Based Cohort Study: Canadian Census Health and Environmental Cohort

Our plain-English summary of Cancer Risks among Welders and Occasional Welders in a National Population-Based Cohort Study: Canadian Census Health and Environmental Cohort, by J.S. MacLeod, M.A. Harris, M. Tjepkema, et al (Safety and Health at Work, 2017).

The study

• Authors: J.S. MacLeod, M.A. Harris, M. Tjepkema, P.A. Peters, P.A. Demers
• Journal: Safety and Health at Work
• Published: 2017;8(3):258-266
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Welders are exposed to many known and suspected carcinogens. An excess lung cancer risk among welders is well established, but whether this is attributable to welding fumes is unclear. Excess risks of other cancers have been suggested, but not established. We investigated welding cancer risks in the population-based Canadian Census Health and Environmental Cohort.

Methods: Among 1.1 million male workers, 12,845 welders were identified using Standard Occupational Classification codes and followed through retrospective linkage of 1991 Canadian Long Form Census and Canadian Cancer Registry (1992-2010) records. Hazard ratios (HRs) were calculated using Cox proportional hazards models based on estimated risks of lung cancer, mesothelioma, and nasal, brain, stomach, kidney, and bladder cancers, and ocular melanoma. Lung cancer histological subtypes and risks by industry group and for occasional welders were examined. Some analyses restricted comparisons to blue-collar workers to minimize effects of potential confounders.

Results: Among welders, elevated risks were observed for lung cancer [HR: 1.16, 95% confidence interval (CI): 1.03-1.31], mesothelioma (HR: 1.78, 95% CI: 1.01-3.18), bladder cancer (HR: 1.40, 95% CI: 1.15-1.70), and kidney cancer (HR: 1.30, 95% CI: 1.01-1.67). When restricted to blue-collar workers, lung cancer and mesothelioma risks were attenuated, while bladder and kidney cancer risks increased.

Conclusion: Excess risks of lung cancer and mesothelioma may be partly attributable to factors including smoking and asbestos. Welding-specific exposures may increase bladder and kidney cancer risks, and particular sources of exposure should be investigated. Studies that are able to disentangle welding effects from smoking and asbestos exposure are needed.

In plain English

This retrospective cohort study used the Canadian Census Health and Environmental Cohort, which linked answers to the 1991 long-form census with cancer registry records through 2010. Among 1,108,410 male workers, 12,845 were welders and 87,460 held jobs involving occasional welding, judged from their 1991 job. Compared with nonwelders, welders had a hazard ratio of 1.16 (95% CI 1.03 to 1.31) for lung cancer, 1.78 (1.01 to 3.18) for mesothelioma, based on 15 cases, 1.40 (1.15 to 1.70) for bladder cancer and 1.30 (1.01 to 1.67) for kidney cancer. Occasional welders had a mesothelioma hazard ratio of 1.74 (1.34 to 2.26). When welders were compared only with other blue-collar workers, their lung cancer hazard ratio was 1.06 (0.94 to 1.20), no longer statistically significant. Their mesothelioma risk stayed elevated but was not statistically significant, while bladder and kidney cancer risks rose further. The study had no smoking data, and the authors described asbestos as a possible confounder. The authors concluded that lung cancer risk among welders may be largely due to factors not specific to welding, including asbestos or smoking.

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: Retrospective population-based cohort study (census records linked to cancer registry records)
• Who was studied: 1,108,410 male Canadian workers aged 25 to 74 who answered the 1991 long-form census. Of these, 12,845 were male welders and 87,460 were male occasional welders. Cancers were followed from 1991 to the end of 2010. The 370 female welders were too few for most analyses.
• Exposure: Welding, assigned from the job reported on the 1991 census. Welders were those coded as welders and soldering machine operators. Occasional welders were those in jobs that potentially involve welding, such as plumbers, pipefitters, boilermakers, sheet metal workers and mechanics. Asbestos exposure was not measured directly.
• Main results:
  • Male welders compared with nonwelders: lung cancer HR 1.16 (95% CI 1.03 to 1.31), 265 cases. Mesothelioma HR 1.78 (95% CI 1.01 to 3.18), 15 cases.
  • Male welders compared with other blue-collar workers: lung cancer HR 1.06 (0.94 to 1.20). This was attenuated from the comparison with nonwelders and was no longer statistically significant.
  • Male welders compared with other blue-collar workers: mesothelioma HR 1.54 (0.86 to 2.78). The risk remained elevated but was not statistically significant.
  • Male occasional welders compared with nonwelders: mesothelioma HR 1.74 (1.34 to 2.26), 65 cases, and lung cancer HR 1.12 (1.07 to 1.18). Compared with blue-collar workers, their mesothelioma HR was 1.48 (1.13 to 1.96), which remained significant.
  • Welders in construction compared with nonwelders: mesothelioma HR 2.54 (1.01 to 6.34), 5 cases.
  • Male welders compared with nonwelders: bladder cancer HR 1.40 (1.15 to 1.70), 100 cases. Kidney cancer HR 1.30 (1.01 to 1.67), 60 cases. Compared with blue-collar workers, these were 1.47 (1.21 to 1.79) and 1.34 (1.04 to 1.73).
  • Male welders compared with nonwelders: small cell lung cancer HR 1.54 (1.15 to 2.07), 45 cases. Adenocarcinoma HR 1.12 (0.89 to 1.41) was weaker and not significant.
• The authors' conclusion: The authors concluded that lung cancer risk among welders cannot be attributed exclusively or directly to welding fume exposure. In their view it may be largely attributable to factors not specific to welding, including possible occupational co-exposures such as asbestos, or smoking. They also concluded that bladder and kidney cancer risks among welders should be investigated further.
• Limitations the authors state:
  • Exposure was based on a single self-report of occupation at baseline.
  • It is not known how often welders changed jobs during follow-up, which could misclassify exposure.
  • No smoking data were available.
  • Asbestos exposure may be an even more important confounder than smoking.
  • Because exposure came from job title, the authors could not examine specific materials or welding processes.

Topics

Medical terms in this study, explained in our Lexicon: Cohort Study, Lung Cancer, Cancer Registry, Hazard Ratio, Mesothelioma, Histological Subtype, confidence interval, Asbestos Exposure.

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