Welding fumes and lung cancer: a meta-analysis of case-control and cohort studies

Our plain-English summary of Welding fumes and lung cancer: a meta-analysis of case-control and cohort studies, by M.K. Honaryar, R.M. Lunn, D. Luce, et al (Occupational and Environmental Medicine, 2019).

The study

• Authors: M.K. Honaryar, R.M. Lunn, D. Luce, W. Ahrens, A. 't Mannetje, J. Hansen, L. Bouaoun, D. Loomis, G. Byrnes, N. Vilahur, L. Stayner, N. Guha
• Journal: Occupational and Environmental Medicine
• Published: 2019;76(6):422-431
• Type of article: Meta-analysis, Systematic review
• Cited by: 48 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: An estimated 110 million workers are exposed to welding fumes worldwide. Welding fumes are classified by the International Agency for Research on Cancer as carcinogenic to humans (group 1), based on sufficient evidence of lung cancer from epidemiological studies.

Objective: To conduct a meta-analysis of case-control and cohort studies on welding or exposure to welding fumes and risk of lung cancer, accounting for confounding by exposure to asbestos and tobacco smoking.

Methods: The literature was searched comprehensively in PubMed, reference lists of relevant publications and additional databases. Overlapping populations were removed. Meta-relative risks (mRRs) were calculated using random effects models. Publication bias was assessed using funnel plot, Eggers's test and Begg's test.

Results: Forty-five studies met the inclusion criteria (20 case-control, 25 cohort/nested case-control), which reduced to 37 when overlapping study populations were removed. For 'ever' compared with 'never' being a welder or exposed to welding fumes, mRRs and 95% CIs were 1.29 (1.20 to 1.39; I2=26.4%; 22 studies) for cohort studies, 1.87 (1.53 to 2.29; I2=44.1%; 15 studies) for case-control studies and 1.17 (1.04 to 1.38; I2=41.2%) for 8 case-control studies that adjusted for smoking and asbestos exposure. The mRRs were 1.32 (95% CI 1.20 to 1.45; I2=6.3%; 15 studies) among 'shipyard welders', 1.44 (95% CI 1.07 to 1.95; I2=35.8%; 3 studies) for 'mild steel welders' and 1.38 (95% CI 0.89 to 2.13; I2=68.1%; 5 studies) among 'stainless steel welders'. Increased risks persisted regardless of time period, geographic location, study design, occupational setting, exposure assessment method and histological subtype.

Conclusions: These results support the conclusion that exposure to welding fumes increases the risk of lung cancer, regardless of the type of steel welded, the welding method (arc vs gas welding) and independent of exposure to asbestos or tobacco smoking.

© Author(s) (or their employer(s)) 2019. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This article was a meta-analysis, which pools results from earlier published studies, of welding or welding fumes and lung cancer. It was done alongside the International Agency for Research on Cancer's 2017 re-evaluation. Of 45 eligible studies, 37 remained after overlapping populations were removed. Compared with people never welders or exposed to welding fumes, the pooled relative risk of lung cancer was 1.43 (95% CI 1.31 to 1.55) across 37 studies. It was 1.29 (95% CI 1.20 to 1.39) in 22 cohort studies and 1.87 (95% CI 1.53 to 2.29) in 15 case-control studies. In 8 studies adjusted for both smoking and asbestos exposure it was 1.17 (95% CI 1.04 to 1.38). In 15 studies of shipyard welders it was 1.32 (95% CI 1.20 to 1.45). Risk rose with years employed as a welder, although that analysis used only two studies. Tests suggested possible publication bias. The authors concluded that lung cancer risk was increased independent of smoking and asbestos exposure, regardless of welding method or metal welded. They noted that welding fumes were often not measured directly.

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: Meta-analysis (labelled a review) of published case-control, nested case-control and cohort studies, conducted in parallel with the IARC Monograph 118 re-evaluation
• Who was studied: 45 eligible studies (20 case-control, 25 cohort/nested case-control), reduced to 37 after removing overlapping populations. They covered 16 485 328 cohort participants, plus 137 624 cases and 364 555 controls from case-control studies. The literature search ran up to 28 March 2017.
• Exposure: Ever having been a welder or exposed to welding fumes, compared with never. Smoking and asbestos exposure were treated as confounders. Subgroups covered mild steel, stainless steel, arc and gas welding, and shipyard work.
• Main results:
  • All 37 studies combined: pooled relative risk (mRR) of lung cancer 1.43 (95% CI 1.31 to 1.55) for ever versus never welders or exposed to welding fumes
  • 8 studies that adjusted for smoking and asbestos exposure simultaneously: mRR 1.17 (95% CI 1.04 to 1.38)
  • 11 studies that adjusted for asbestos: mRR 1.22 (95% CI 1.09 to 1.32)
  • Cohort studies: mRR 1.29 (95% CI 1.20 to 1.39; 22 studies). Cohorts adjusted for smoking: mRR 1.10 (95% CI 1.06 to 1.14; 6 studies).
  • Case-control studies: mRR 1.87 (95% CI 1.53 to 2.29; 15 studies)
  • Shipyard welders: mRR 1.32 (95% CI 1.20 to 1.45; 15 studies)
  • Mild steel welders: mRR 1.44 (95% CI 1.07 to 1.95; 3 studies)
  • Stainless steel welders: mRR 1.38 (95% CI 0.89 to 2.13). The confidence interval included 1.
  • Exclusively gas welding: mRR 1.71 (95% CI 1.10 to 2.66; 3 studies). Exclusively arc welding: mRR 1.36 (95% CI 0.70 to 2.67; 2 studies).
  • Duration of employment as a welder was statistically significantly associated with lung cancer risk (p=0.001 and 0.009). This exposure-effect analysis was based on two studies.
  • The funnel plot suggested more small studies with positive findings than expected. Egger's and Begg's tests both suggested asymmetry, a possible sign of publication bias.
• The authors' conclusion: The authors concluded that lung cancer risk was significantly increased, independent of tobacco smoking and asbestos exposure, regardless of welding method (arc or gas) and type of metal welded, and that it increased with duration of welding. They stated this supports IARC's classification of welding fumes as carcinogenic to humans (group 1).
• Limitations the authors state:
  • The authors could not estimate lung cancer risk by quantitative level of exposure to welding fumes.
  • The exposure-effect analysis was based on only two studies, and its wide confidence intervals limit interpretation.
  • Welding processes could not be distinguished in greater detail.
  • 'Ever welder' was a crude exposure category and was defined differently across studies.
  • In some studies the reference group was not precisely defined.
  • Some studies used other occupational groups, such as other metal workers, as the reference group, which the authors said would underestimate the risk.
  • Publication bias could have led to overestimation of the pooled risk for ever welders.
  • Welding fumes were often not measured directly but were assessed indirectly, for example through job title, expert assessment or self-report.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Welders.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Meta-Analysis, Carcinogenic, Confounding, Relative Risk, Asbestos Exposure, Histological Subtype.

Related studies

• Heavy metals, welding fumes, and other occupational exposures, and the risk of kidney cancer: A population-based nested case-control study in three Nordic countries — I.M. Michalek, J.I. Martinsen, et al. (2019)
• Exposure to stainless steel welding fumes and lung cancer: a meta-analysis — B. Sjögren, K.S. Hansen, et al. (1994)
• Lung cancer risk and welding: results from a case-control study in Germany — K.H. Jöckel, W. Ahrens, et al. (1998)
• Lung cancer risk and welding--preliminary results from an ongoing case-control study — K.H. Jöckel, W. Ahrens, et al. (1994)
• Response of bovine alveolar macrophages in vitro to welding fume particles — L.R. White, A.B. Marthinsen, et al. (1983)
• Inter-rater agreement for a retrospective exposure assessment of asbestos, chromium, nickel and welding fumes in a study of lung cancer and ionizing radiation — E.A. Seel, D.D. Zaebst, et al. (2007)

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