Esophagus cancer and occupational exposure to asbestos: results from a meta-analysis of epidemiology studies

Our plain-English summary of Esophagus cancer and occupational exposure to asbestos: results from a meta-analysis of epidemiology studies, by B. Li, S.P. Tang, K.Z. Wang (Diseases of the Esophagus, 2016).

The study

• Authors: B. Li, S.P. Tang, K.Z. Wang
• Journal: Diseases of the Esophagus
• Published: 2016;29(5):421-8
• Type of article: Meta-analysis
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The relationship between occupational asbestos exposure and esophagus cancer (EC) is not fully understood. We performed a meta-analysis to quantitatively assess the association. We systematically searched databases of PubMed, EMBASE, and Web of Science for studies with quantitative estimates of asbestos exposure and EC mortality. Pooled standardized mortality ratios (SMRs) and their corresponding 95% confidence intervals (CIs) were calculated. Twenty cohort studies on EC and asbestos exposure were included in this meta-analysis. Overall, occupational exposure to asbestos was associated with an excess risk of EC (SMR = 1.24, 95% CI: 1.13-1.38, P < 0.001), with little evidence of heterogeneity among studies (I(2) = 0.0%, P = 0.682). Being male, exposure to chrysotile or mixed asbestos, working at textile industry, long study follow-up (≥20 years), Asia, Europe and America cohorts with larger cohort size (>500), and high-exposure group all contribute to significantly higher SMR. Publication bias was not detected (Egger's test P-value = 0.374). This meta-analysis suggested that occupational asbestos exposure might be associated with an increased risk of EC in male. High-exposure level of asbestos could contribute to significantly higher risk of EC mortality.

© 2015 International Society for Diseases of the Esophagus.

In plain English

This meta-analysis pooled earlier studies found in PubMed, EMBASE and Web of Science up to May 2014. It included 20 cohort studies of asbestos-exposed workers (21 worker groups) in Asia, Europe, the United States and Oceania. Combining studies of esophagus (food pipe) cancer deaths and new cases, these workers had more esophagus cancer than expected, with a pooled ratio of 1.24 (95% confidence interval 1.12 to 1.37 in the results text, 1.13 to 1.38 in the summary and table). For deaths alone the ratio was 1.22 (1.10 to 1.36). In separate analyses, the ratio was 1.53 (1.22 to 1.91) for males, 1.33 (1.02 to 1.74) for chrysotile-only cohorts and 1.52 (1.17 to 1.97) for textile workers. Results for crocidolite cohorts, miners and shipyard workers were not statistically significant. Five studies of the most highly exposed workers gave 2.09 (1.46 to 3.00). The authors concluded that occupational asbestos exposure might be associated with increased esophagus cancer risk in males. They noted their estimates were not adjusted for other risk factors and called for studies to establish causation.

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 (pooled analysis) of published cohort studies, using standardized mortality ratios (SMRs) or standardized incidence ratios
• Who was studied: 20 cohort studies (21 distinct worker populations) found in PubMed, EMBASE and Web of Science, published in English or Chinese between 1988 and 2014. Cohort sizes ranged from 249 to 98,117. The text lists six studies from Asia, seven from Europe, four from the United States and three from Oceania.
• Exposure: Occupational asbestos exposure: crocidolite, chrysotile, amosite (printed 'amesite' in the text) and mixed asbestos. The industries were mining, textiles, refitting shipyard, reprocessing plant and others.
• Main results:
  • All studies pooled (mortality and incidence studies combined): SMR for esophagus cancer of 1.24 (95% CI 1.12 to 1.37, P less than 0.001), which the authors called statistically significant. The summary and Table 2 print the interval as 1.13 to 1.38.
  • Mortality studies only (19): SMR 1.22 (95% CI 1.10 to 1.36). Incidence studies only (3): 1.37 (95% CI 1.02 to 1.85).
  • Asbestos-exposed males: SMR 1.53 (95% CI 1.22 to 1.91). Table 2 lists 12 studies in this group. Data on females were too limited for analysis.
  • Cohorts exposed only to chrysotile: SMR 1.33 (95% CI 1.02 to 1.74, P = 0.034). Mixed asbestos: SMR 1.24 (95% CI 1.11 to 1.39).
  • Crocidolite cohorts (3 studies): SMR 1.07 (95% CI 0.70 to 1.64, P = 0.751), not statistically significant.
  • Textile workers: SMR 1.52 (95% CI 1.17 to 1.97, P = 0.002). The pooled SMR was not significantly elevated for miners (1.14, 95% CI 0.88 to 1.52) or shipyard workers (1.59, 95% CI 0.98 to 2.59).
  • By region, pooled SMRs were increased for Asia (1.38), Europe (1.22) and the United States (1.57). Oceania cohorts showed no apparent increase (SMR 1.01, 95% CI 0.68 to 1.49).
  • The five studies reporting the highest-exposed groups (by cumulative exposure or duration) gave a pooled SMR of 2.09 (95% CI 1.46 to 3.00).
  • Removing the largest study (Harding et al.) gave a combined SMR of 1.36 (95% CI 1.17 to 1.58).
  • Tests for publication bias gave P-values of 0.291 (Begg's) and 0.374 (Egger's), which the authors said provided little evidence of publication bias.
• The authors' conclusion: The authors concluded that occupational asbestos exposure might be associated with an increased risk of esophagus cancer in males. They said further large-scale, long-term studies that control for confounding factors are needed to establish a possible causal relation.
• Limitations the authors state:
  • The included studies lacked data on other risk factors, so the analysis used unadjusted estimates.
  • Studies defined exposure duration or latency differently, which prevented a proper dose-response evaluation.
  • Too few studies reported on women to estimate their risk.
  • Limited data meant no analysis by esophagus cancer subtype.

Topics

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

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Meta-Analysis, Epidemiology, Asbestos Exposure, standardized mortality ratio (SMR), confidence interval, Chrysotile, P-Value.

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