Occupational asbestos exposure and urinary bladder cancer: a systematic review and meta-analysis

Our plain-English summary of Occupational asbestos exposure and urinary bladder cancer: a systematic review and meta-analysis, by N. Franco, A. Godono, M. Clari, et al (World Journal of Urology, 2023).

The study

• Authors: N. Franco, A. Godono, M. Clari, C. Ciocan, C. Zunarelli, E. Pira, P. Boffetta
• Journal: World Journal of Urology
• Published: 2023;41(4):1005-1015
• Type of article: Meta-analysis, Systematic review
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: There is conflicting evidence on the association between asbestos exposure and bladder cancer. We performed a systematic review and meta-analysis to provide evidence on occupational asbestos exposure and the risk of mortality and incidence of bladder cancer.

Methods: We searched three relevant electronic databases (Pubmed, Scopus, and Embase) from inception to October 2021. The methodological quality of included articles was evaluated using the US National Institutes of Health tool. Standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs) for bladder cancer, as well as respective 95% confidence intervals (CIs), were extracted or calculated for each included cohort. Main and subgroup meta-analyses according to first year of employment, industry, sex, asbestos type, and geographic region were performed.

Results: Fifty-nine publications comprising 60 cohorts were included. Bladder cancer incidence and mortality were not significantly associated with occupational asbestos exposure (pooled SIR: 1.04, 95% CI: 0.95-1.13, P = 0.000; pooled SMR: 1.06, 95% CI: 0.96-1.17, P = 0.031). Bladder cancer incidence was higher among workers employed between 1908 and 1940 (SIR: 1.15, 95% CI: 1.01-1.31). Mortality was elevated in asbestos workers cohorts (SMR: 1.12, 95% CI: 1.06-1.30) and in the subgroup analysis for women (SMR: 1.83, 95% CI: 1.22-2.75). No association was found between asbestos types and bladder cancer incidence or mortality. We observed no difference in the subgroup analysis for countries and no direct publication bias evidence.

Conclusion: There is evidence that workers with occupational asbestos exposure have a bladder cancer incidence and mortality similar to the general population.

© 2023. The Author(s).

In plain English

This systematic review and meta-analysis pooled published cohort and nested case-control studies of bladder cancer in workers with respiratory occupational exposure to asbestos. It included 59 publications covering 60 cohorts, with 3596 bladder cancer cases among 525,585 subjects and 1169 bladder cancer deaths among 385,552 subjects. Overall, bladder cancer incidence (pooled SIR 1.04, 95% CI 0.95–1.13) and mortality (pooled SMR 1.06, 95% CI 0.96–1.17) were not significantly raised compared with the general population. Some subgroups had higher figures. Incidence was higher among workers first employed between 1908 and 1940 (SIR 1.15, 95% CI 1.01–1.31). The authors said this result should be interpreted with caution because it came from multiple stratified analyses. Mortality was higher among women (SMR 1.83, 95% CI 1.22–2.75, based on 27 deaths) and in asbestos workers cohorts (SMR 1.12, 95% CI 1.06–1.30). Results split by asbestos type matched the overall finding. The authors concluded that exposed workers had bladder cancer incidence and mortality similar to the general population, and they judged the excess in women unlikely to be causal. They noted that the studies lacked smoking data, so the pooled figures could be overestimated.

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: Systematic review and meta-analysis (random-effects) of cohort and nested case-control studies
• Who was studied: 59 publications comprising 60 cohorts of occupationally exposed workers in Europe, the UK, North America, Australia and Asia. Bladder cancer incidence was studied in 26 cohorts and mortality in 38. In total there were 3596 bladder cancer cases out of 525,585 subjects and 1169 bladder cancer deaths out of 385,552 subjects.
• Exposure: Respiratory occupational exposure to asbestos in any industry or occupation, including asbestos workers, miners and millers, shipyards and insulation work. Studies of workers with only possible exposure (such as electricity workers or chimney sweeps) were kept only if their mesothelioma SMR or SIR was above 2. Asbestos type was grouped as amphiboles, chrysotile, mixed, or unspecified.
• Main results:
  • Across all cohorts, bladder cancer incidence (pooled SIR 1.04, 95% CI 0.95–1.13) and mortality (pooled SMR 1.06, 95% CI 0.96–1.17) were not significantly associated with occupational asbestos exposure.
  • Bladder cancer incidence was higher among workers first employed between 1908 and 1940 (SIR 1.15, 95% CI 1.01–1.31; 9 studies).
  • Bladder cancer mortality was higher among women (SMR 1.83, 95% CI 1.22–2.75). The authors said this result was based on five studies with a total of 27 observed deaths.
  • Bladder cancer mortality was higher in the asbestos workers subgroup (SMR 1.12, 95% CI 1.06–1.30; 13 studies).
  • Subgroup analyses by type of asbestos fibers, country and study quality gave results in line with the overall finding.
  • In a meta-analysis of meta-regressions covering 5 studies, the risk ratio per year of exposure was 0.97 (CI 0.905–1.041) for mortality and 1.019 (CI 0.997–1.041) for incidence.
  • No evidence of publication bias was found for either incidence or mortality.
• The authors' conclusion: The authors concluded that their meta-analysis provides evidence that workers with occupational asbestos exposure have bladder cancer incidence and mortality similar to the general population. They added that further studies are needed on female workers.
• Limitations the authors state:
  • The reviewed studies lacked information on smoking, the main risk factor for bladder cancer, so the pooled SMR and SIR could be overestimated.
  • Most cohorts lacked quantitative exposure data. Duration of employment, used as a stand-in for dose, was available in only 12 of 60 studies.
  • The higher incidence among workers first employed between 1908 and 1940 should be interpreted with caution because it comes from multiple stratified analyses.
  • The authors judged the excess mortality in women unlikely to be causal. The result was heavily influenced by one study (Ferrante et al.), was not confirmed for incidence among women, and four of the five studies did not consider smoking.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Systematic Review, Meta-Analysis, Standardized Incidence Ratio (SIR), standardized mortality ratio (SMR), confidence interval.

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