Stomach cancer mortality among workers exposed to asbestos: a meta-analysis

Our plain-English summary of Stomach cancer mortality among workers exposed to asbestos: a meta-analysis, by W.J. Peng, X.J. Jia, B.G. Wei, et al (Journal of Cancer Research and Clinical Oncology, 2015).

The study

• Authors: W.J. Peng, X.J. Jia, B.G. Wei, L.S. Yang, Y. Yu, L. Zhang
• Journal: Journal of Cancer Research and Clinical Oncology
• Published: 2015;141(7):1141-9
• Type of article: Meta-analysis, Systematic review
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The relationship between asbestos and stomach cancer is not well understood because of small number of cases. This study aimed to determine the incidence and mortality of stomach cancer among workers exposed to asbestos based on a systematic review and meta-analysis approach.

Methods: Relevant English electronic databases were systematically searched for published studies characterizing the risk of developing stomach cancer as a result of asbestos exposure. Standardized mortality rate (SMR) for stomach cancer with its 95% confidence interval (CI) was pooled using a fixed-/random-effect model in STATA.

Results: A total of 32 independent studies were included for the analysis. The overall SMR for stomach cancer was 1.19 (95% CI 1.06-1.34), with a moderate degree of heterogeneity across the studies (I(2) = 37.6%, P = 0.011). Being male, exposure to crocidolite, miners, studies conducted in Europe and Oceania, and long study follow-up (≥ 25 years) all contribute to significantly higher SMR. Significant publication bias was observed.

Conclusion: Elevated risk of stomach cancer mortality was evidenced among workers exposed to crocidolite, especially male miners.

In plain English

This article was a meta-analysis, a review pooling results of earlier published studies. The authors included 40 cohorts from 32 studies of asbestos-exposed people, mostly in Europe, in industries such as shipyard refitting, mining, textiles and cement. Most studies counted stomach cancer deaths and five counted new cases. Combined, the standardized ratio of observed to expected was 1.19 (95% CI 1.06–1.34). The ratio was significantly raised for men, 1.30 (1.16–1.45). For women it was 0.97 (0.76–1.24), not statistically significant. It was significantly raised for cohorts exposed only to crocidolite, 1.55 (1.27–1.89), and to mixed asbestos, 1.22 (1.06–1.41). For chrysotile it was 0.97 (0.80–1.17), not statistically significant. It was raised for miners, 1.43 (1.20–1.70), and for follow-up of 25 years or more, 1.26 (1.11–1.42). The authors found signs of publication bias. After adjustment, the estimate was smaller but remained significant. The authors concluded that asbestos exposure is associated with an increased risk of stomach cancer, especially in male miners, and that crocidolite is more harmful. They stated they could not analyze smoking, alcohol, other workplace exposures or 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, pooled with a random-effect model
• Who was studied: 40 cohorts from 32 independent cohort studies of asbestos-exposed people. They were selected from 1,327 papers identified in PubMed, Elsevier and Web of Science (English and Chinese language). Most were from Europe, five from Asia, three from America and four from Oceania.
• Exposure: Occupational asbestos exposure in industries mainly including refitting shipyards, mining, textiles and cement. Studies were grouped by fiber type as chrysotile, crocidolite or mixed asbestos.
• Main results:
  • All 32 studies combined (27 mortality studies and 5 incidence studies): the pooled SMR for stomach cancer among asbestos-exposed workers was 1.19 (95% CI 1.06–1.34), with moderate heterogeneity between studies (I2 = 37.6%).
  • Men (25 studies): pooled SMR 1.30 (95% CI 1.16–1.45). Women (11 studies): pooled SMR 0.97 (95% CI 0.76–1.24), p = 0.788, not statistically significant.
  • Cohorts exposed only to crocidolite (4 studies): pooled SMR 1.55 (95% CI 1.27–1.89). Mixed asbestos (19 studies): 1.22 (95% CI 1.06–1.41). Chrysotile (9 studies): 0.97 (95% CI 0.80–1.17), not statistically significant.
  • Mining workers (6 studies): pooled SMR 1.43 (95% CI 1.20–1.70). The textile, cement, shipyard and mixed-industry subgroups were not statistically significant.
  • Studies with follow-up of 25 years or more (25 studies): pooled SMR 1.26 (95% CI 1.11–1.42). Follow-up under 25 years (7 studies): 0.97 (95% CI 0.79–1.19).
  • By region, the pooled SMR was raised for European cohorts (1.21, 95% CI 1.05–1.40) and Oceanian cohorts (1.53, 95% CI 1.26–1.86). Asian and American cohorts appeared to show no increase.
  • The five incidence studies pooled to 1.21 (95% CI 0.97–1.52), p = 0.094, not statistically significant. The mortality studies alone pooled to 1.19 (95% CI 1.04–1.35).
  • In meta-regression, gender and follow-up period explained the differences between studies. Fiber type, outcome type, region, industry and sample size did not.
  • Leaving out any single study did not significantly change the pooled result.
  • The funnel plot was not symmetrical, suggesting publication bias. After trim-and-fill adjustment, the estimate was attenuated but remained significant (data not shown).
• The authors' conclusion: The authors concluded that exposure to asbestos is associated with an increased risk of stomach cancer, especially in male miners, and that crocidolite is more harmful to humans. They called for further work to clarify the association.
• Limitations the authors state:
  • The available data did not allow analysis by confounding factors such as alcohol and smoking, other occupational exposures, or fiber diameter.
  • A dose-response analysis could not be done because the original cohorts gave limited data.
  • Significant publication bias was observed, so the authors said the results should be interpreted with caution.

Topics

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

Medical terms in this study, explained in our Lexicon: Stomach Cancer, Meta-Analysis, Systematic Review, Asbestos Exposure, confidence interval, Crocidolite.

Related studies

• Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers — K. Straif, U. Keil, et al. (2000)
• Occupational risk factors for mortality from stomach and lung cancer among rubber workers: an analysis using internal controls and refined exposure assessment — K. Straif, L. Chambless, et al. (1999)
• Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa — J.L. Botha, L.M. Irwig, et al. (1986)
• Re: "Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa" — H.P. Hart (1987)
• Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies — L. Fortunato, L. Rushton (2015)
• Talc exposure and risk of stomach cancer: Systematic review and meta-analysis of occupational cohort studies — C.J. Chang, Y.K. Tu, et al. (2020)

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