The association between occupational asbestos exposure with the risk of incidence and mortality from prostate cancer: a systematic review and meta-analysis

Our plain-English summary of The association between occupational asbestos exposure with the risk of incidence and mortality from prostate cancer: a systematic review and meta-analysis, by A. Godono, M. Clari, N. Franco, et al (Prostate Cancer and Prostatic Diseases, 2022).

The study

• Authors: A. Godono, M. Clari, N. Franco, C. Ciocan, I. Mansour, C. Zunarelli, E. Pira, P. Boffetta
• Journal: Prostate Cancer and Prostatic Diseases
• Published: 2022;25(4):604-614
• Type of article: Meta-analysis, Systematic review
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: There is conflicting evidence on the association between asbestos exposure and prostate cancer (PCa). Two recent meta-analyses have claimed that exposure is associated with increased PCa incidence and mortality, but they suffer from some methodological flaws. Given the potential importance of this research question, we aimed to perform a methodologically sound systematic review and meta-analysis to investigate the association between occupational asbestos exposure and the incidence of and mortality from PCa.

Methods: We followed PRISMA guidelines to systematically search for pertinent articles in three relevant electronic databases: Pubmed, Scopus, and Embase, from their inception to July 2020. 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 PCa, 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, asbestos type, and geographic region were performed.

Results: Sixty-five articles comprising 68 cohorts were included. PCa incidence and mortality were not significantly associated with occupational asbestos exposure (pooled SIR: 1.06, 95% CI: 1.00-1.13, P = 0.062; pooled SMR: 1.03, 95% CI: 0.99-1.06, P = 0.115). PCa incidence was higher among workers employed after 1960 (SIR: 1.10, 95% CI: 1.01-1.20). Pooled SIR was elevated in European (SIR: 1.09, 95% CI: 1.01-1.18) and UK cohorts (SIR: 1.05, 95% CI: 1.02-1.09). Mortality was elevated in North American cohorts (SMR: 1.06, 95% CI: 1.02-1.10). Studies of lower methodological quality appeared to yield elevated SIRs or SMRs.

Conclusions: This systematic review and meta-analysis provides evidence that men with occupational asbestos exposure have a PCa incidence and mortality similar to that of the general population. Temporal and geographical variables seem to be related to higher SMR or SIR.

© 2021. The Author(s), under exclusive licence to Springer Nature Limited.

In plain English

This was a systematic review and meta-analysis. The authors searched three databases to July 2020 and included 65 articles on 68 cohorts of men who breathed asbestos at work; two cohorts with no prostate cancer cases or deaths were not pooled. Most cohorts were European or North American. They compared prostate cancer diagnoses and deaths with general-population expectations. Overall, neither was statistically significantly raised: pooled incidence ratio 1.06 (95% CI 1.00–1.13), pooled mortality ratio 1.03 (95% CI 0.99–1.06). Higher incidence appeared in men first employed in 1960–1993 (1.10, 95% CI 1.01–1.20), shipyard workers (1.18, 95% CI 1.04–1.33), and European (1.09, 95% CI 1.01–1.18) and UK (1.05, 95% CI 1.02–1.09) cohorts. North American cohorts showed higher mortality (1.06, 95% CI 1.02–1.10). The Asia and Australia subgroup showed lower incidence (0.67, 95% CI 0.60–0.75); its incidence data came from two Asian cohorts, one carrying 97% of the weight. Lower-quality studies tended to report raised figures. No association was found with asbestos type, which few studies reported. The authors concluded that exposed workers have prostate cancer incidence and mortality similar to the general population.

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 of published cohort studies (and one nested case-control study), following PRISMA guidelines
• Who was studied: 65 articles reporting on 68 cohorts of men with respiratory occupational asbestos exposure, published 1981 to 2020, found by searching Pubmed, Scopus and Embase to July 20, 2020. Cohorts came from Europe (39), North America (18), Asia and Australia (7) and the UK (6).
• Exposure: Occupational asbestos exposure by inhalation in industries such as insulation, shipyards, asbestos mining and milling, and asbestos product work. Cohorts from industries with only possible exposure were included if their mesothelioma SIR or SMR was above 2. Asbestos type was reported in only 15 articles, most often chrysotile (9).
• Main results:
  • Two of the 68 cohorts could not be included in the meta-analysis because they reported no prostate cancer cases or deaths. These were one of the two Tomioka et al. cohorts and the cohort of one additional article.
  • Overall, prostate cancer incidence and mortality were not significantly associated with occupational asbestos exposure: pooled SIR 1.06 (95% CI 1.00–1.13, P = 0.062); pooled SMR 1.03 (95% CI 0.99–1.06, P = 0.115).
  • The pooled incidence estimate showed significant differences between studies (I2 = 78.4%). No such differences were found for the pooled mortality estimate (I2 = 0%).
  • Prostate cancer incidence was higher among workers employed after 1960 (the 1960–1993 first-employment stratum in Table 2): SIR 1.10 (95% CI 1.01–1.20).
  • Among shipyard workers, the pooled prostate cancer incidence ratio was 1.18 (95% CI 1.04–1.33).
  • Pooled incidence ratios by region: Europe 1.09 (95% CI 1.01–1.18), UK 1.05 (95% CI 1.02–1.09), Asia and Australia 0.67 (95% CI 0.60–0.75).
  • The Asia and Australia incidence estimate rested on two cohorts (Table 2). In Table 1 both incidence cohorts are listed under Asia (Lin et al. and Wu et al.); the two Australian cohorts reported mortality. The authors noted the Asian findings were mainly based on one study, which carried 97% of the weight in this subgroup.
  • The highest prostate cancer mortality was in North American cohorts: SMR 1.06 (95% CI 1.02–1.10).
  • In a sensitivity analysis, removing the Lin et al. study raised the pooled incidence ratio to 1.09 (95% CI 1.04–1.14). Removing any single article did not change the pooled mortality ratios, which ranged from 1.01 to 1.05.
  • Articles of poor methodological quality reported increased prostate cancer incidence and mortality (poor-quality subgroup in Table 2: SMR 1.06, 95% CI 1.02–1.11; SIR 1.12, 95% CI 1.01–1.24). Results were consistent among medium- and high-quality articles.
  • No association was found between specific asbestos type and prostate cancer incidence or mortality.
  • No direct evidence of publication bias was observed for prostate cancer incidence or mortality.
• The authors' conclusion: The authors concluded that their meta-analysis provides evidence that workers with occupational asbestos exposure have prostate cancer incidence and mortality similar to the general population. They called for further studies on different asbestos types and on under-studied regions such as Asia.
• Limitations the authors state:
  • Study quality varied, and data such as duration of employment, person-years and age distribution were not always available.
  • A meta-regression on duration of employment could not be interpreted because too few studies provided these data.
  • Few studies reported asbestos type and cumulative exposure, so understanding of effects by asbestos type is likely limited.
  • Some recent studies were mainly based on young workers, and further follow-up is needed.
  • The findings for Asia rested mainly on a single study, which accounted for 97% of the weight in that subgroup.

Topics

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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