Does exposure to asbestos cause prostate cancer? A systematic literature review and meta-analysis

Our plain-English summary of Does exposure to asbestos cause prostate cancer? A systematic literature review and meta-analysis, by R. Peng, F. Fang, Z. Chen, et al (Medicine, 2019).

The study

• Authors: R. Peng, F. Fang, Z. Chen, S. Yang, C. Dai, C. Wang, H. Guan, Q. Li
• Journal: Medicine
• Published: 2019;98(3):e14108
• Type of article: Meta-analysis, Systematic review
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: The relationship between asbestos and prostate cancer (PCa) is not well understood due to small number of cases. This study aimed to determine the incidence and mortality of PCa among workers or residents exposed to asbestos based on a systematic review and meta-analysis METHODS: All published studies citing the standardized mortality ratio (SMR) or standardized incidence ratio (SIR) of PCa in workers or residents exposed to asbestos were collected by conducting a search on PubMed, EMBASE, Cochrane Library, and Web of Science before April 2018. Standardized mortality rate for PCa with its 95% confidence interval (CI) was pooled using a fixed-/random-effect model in STATA (Version14.0). This study is registered with PROSPERO, number CRD42018095195.

Results: A total of 17 independent studies were included for the analysis. The overall pooled SMR of PCa was 1.22, with a 95% CI of 1.13 to 1.32, with no heterogeneity across the studies (I = 18.8%, P = .234). Subgroup analysis shows that exposure to crocidolite, cement, studies conducted in Europe and Oceania, and long study follow-up (≥25 years) all contribute to significantly higher SMR, and we found no evidence of publication bias (Begg test P value = .592, Egger test P value = .874).

Conclusions: This meta-analysis suggested that exposed to asbestos might be associated with an increased risk of PCa. High-exposure level of asbestos could contribute to significantly higher risk of PCa mortality.

In plain English

This was a systematic review and meta-analysis. The authors searched four databases up to April 2018 and combined 17 published cohort studies (1988 to 2017). Most covered asbestos-exposed workers, mainly in Europe; one covered residents of Australian houses insulated with asbestos. Each study compared observed prostate cancer deaths or cases with expected numbers. Pooled together, the ratio was 1.22 (95% CI 1.13 to 1.32). Only 4 of the 17 studies had found a significant link on their own. The 12 mortality studies alone gave 1.10 (0.92 to 1.32), which was not statistically significant. The 5 incidence studies gave 1.25 (1.15 to 1.36). Cement workers (2 studies) had 1.38 (95% CI 1.03 to 1.84 in the table, 1.08 to 1.84 in the text). Chrysotile cohorts (3 studies) had 1.10 (0.87 to 1.39), which was not statistically significant. The article's text and table give conflicting figures for crocidolite and mixed asbestos. The authors concluded that asbestos exposure is associated with increased prostate cancer risk, especially among cement workers. They could not account for smoking, alcohol or other workplace exposures, or study dose-response.

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 reporting standardized mortality ratios (SMR) or standardized incidence ratios (SIR) for prostate cancer
• Who was studied: 17 cohort studies of asbestos-exposed workers or residents, selected from 802 papers found in PubMed, EMBASE, Cochrane Library and Web of Science before April 2018. The studies were published 1988 to 2017, with cohort sizes from 249 to 504660. Most were from Europe, 4 from Oceania, 2 from Asia (China, Japan) and 1 from the USA.
• Exposure: Asbestos exposure classed as chrysotile, crocidolite or mixed. Settings were mines, textile, cement, a refitting shipyard, a refinery and petrochemical plant, and other industries, plus one study of residents of houses insulated with asbestos (largely amosite with some crocidolite).
• Main results:
  • Pooled ratio for prostate cancer across all 17 studies (fixed-effect model): 1.22 (95% CI 1.13 to 1.32), with no heterogeneity (I2 = 18.8%)
  • Only 4 of the 17 individual studies reported a significant association with prostate cancer risk
  • By outcome: the 12 mortality studies pooled to 1.10 (95% CI 0.92 to 1.32, P = .311), which was not statistically significant. The 5 incidence studies pooled to 1.25 (95% CI 1.15 to 1.36).
  • By asbestos type, the text gives crocidolite-exposed workers 1.68 (95% CI 1.06 to 2.64) and chrysotile-exposed workers 1.10 (95% CI 0.87 to 1.39; 3 studies, not significant). Table 2 instead gives crocidolite 1.22 (1.13 to 1.32) and mixed asbestos 1.68 (1.06 to 2.64).
  • By industry: cement workers (2 studies) pooled SMR 1.38 (95% CI given as 1.03 to 1.84 in Table 2 and 1.08 to 1.84 in the text, P = .032). Mixed-industry workers had 1.24 (1.13 to 1.35). The results for miners (1.17, 0.95 to 1.45), textile workers (1.08, 0.42 to 2.76) and other workers (0.89, 0.59 to 1.33) were not statistically significant.
  • By region: Oceania 1.35 (95% CI 1.14 to 1.60) and Europe 1.20 (1.10 to 1.31). Asia (2 studies) was 1.90, not statistically significant (CI 0.44 to 8.23 in Table 2, 0.44 to 8.32 in the text).
  • By follow-up: studies with less than 25 years of follow-up had 1.18 (95% CI 1.08 to 1.30). Studies with 25 years or more had 1.31 (95% CI 1.14 to 1.49).
  • The single study of residents of houses insulated with asbestos reported an SIR for prostate cancer of 1.29 (95% CI 1.07 to 1.54)
  • No evidence of publication bias was found (Begg P = .592, Egger P = .874). Leaving out one study at a time did not significantly change the pooled result.
• The authors' conclusion: The authors concluded that asbestos exposure is associated with an increased risk of prostate cancer, especially among cement workers, and that crocidolite is more harmful. Their abstract states this more cautiously: asbestos exposure "might be associated" with increased risk.
• Limitations the authors state:
  • Limited data prevented analysis by smoking, alcohol or occupational exposure to other substances
  • A dose-response analysis could not be done
  • Data from personal interviews using questionnaires may be affected by individual biases
  • Other unknown or unreported occupational hazards might lead to overestimating the risk from asbestos
  • Some studies did not report prostate cancer, or reported SMRs without confidence intervals
  • Only one US study was included, which may increase selection bias

Topics

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

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