Meta-Analysis of the Association between Asbestos Exposure and Esophageal Cancer

Our plain-English summary of Meta-Analysis of the Association between Asbestos Exposure and Esophageal Cancer, by C.W. Wu, H.Y. Chuang, D.L. Tsai, et al (International Journal of Environmental Research and Public Health, 2021).

The study

• Authors: C.W. Wu, H.Y. Chuang, D.L. Tsai, T.Y. Kuo, C.C. Yang, H.C. Chen, C.H. Kuo
• Journal: International Journal of Environmental Research and Public Health
• Published: 2021;18(21)
• Type of article: Meta-analysis
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: We conducted a meta-analysis to quantitatively assess the association between asbestos exposure and esophageal cancer.

Methods: We systematically collected articles from three electronic databases and calculated the pooled standardized mortality rate (SMR) from the meta-analysis. Subgroup analysis according to the type of asbestos exposure, follow-up years, sample size, industry classification, sex, and high-dose exposure was conducted.

Results: From 242 studies, 34 cohort studies were included in our meta-analysis. Pooled SMR was positively associated with asbestos exposure and esophageal cancer (pooled SMR = 1.28; 95% confidence interval (CI) 1.19-1.38, p < 0.00001). In the subgroup analysis, (1) chrysolite, (2) four groups with follow-up over ten years, (3) the textile industry and shipyard, (4) both male and female, and (5) eight studies on highest asbestos exposure, all the subgroups showed significantly increased pooled SMRs.

Conclusion: Asbestos exposure was significantly and positively associated with esophageal cancer, especially chrysolite. Considering the long latency period, we suggest that patients should be followed up for cancer, including esophageal cancer, for over ten years.

In plain English

In this meta-analysis, the authors pooled 34 cohort studies, published 1963 to 2017, comparing esophageal cancer deaths in asbestos-exposed people with deaths expected from a reference population. The pooled standardized mortality ratio (SMR) was 1.28 (95% confidence interval 1.19–1.38; ranges below are also 95% intervals). The authors described this as exposed participants being 1.28 times more likely to die from esophageal cancer than the general population. The pooled SMR was significantly raised for chrysotile (spelled "chrysolite" in the article's text) at 1.27 (1.07–1.51). It was not significantly raised for amosite (1.14, 0.53–2.47) or crocidolite (1.20, 0.70–2.05). It was significantly raised for textile (1.45, 1.13–1.86) and shipyard workers (1.39, 1.15–1.68), but not significantly among miners (1.07, 0.81–1.41). It was significantly raised for females (1.61, 1.07–2.42), males (1.37, 1.21–1.55) and, across eight studies, the highest-exposure groups (1.84, 1.27–2.68). Studies with 10 years or less of follow-up showed no significant increase. Every included study was rated at high risk of confounding bias because potential confounders were not adjusted for. The authors concluded that asbestos exposure might significantly increase esophageal cancer risk.

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 cohort studies (fixed-effect model, pooling standardized mortality ratios)
• Who was studied: 34 cohort studies (36 SMRs) of asbestos-exposed people, published 1963 to 2017. They were selected from 242 articles found in PubMed, Embase and Web of Science (searched May 16, 2021) and by reference screening. 50 studies were included in the qualitative synthesis. Populations included asbestos-cement, textile, shipyard, insulation, pipe trade and removal workers, miners, and population-based groups in several countries.
• Exposure: Occupational or environmental asbestos exposure as defined by each included study. The fiber subgroups were 7 studies of chrysotile (called "chrysolite" in the text), 4 of amosite, 2 of crocidolite and 20 of mixed asbestos; one included study concerned tremolite. Subgroups were also formed by industry (textile, shipyard, mining) and by highest-exposure groups.
• Main results:
  • All studies combined: the pooled SMR of esophageal cancer in asbestos-exposed participants, compared with the reference group, was 1.28 (95% CI 1.19–1.38; p less than 0.00001).
  • Heterogeneity among studies was not significant (I2 = 20%, p = 0.15).
  • Chrysotile ("chrysolite") subgroup: pooled SMR 1.27 (95% CI 1.07–1.51, p = 0.006).
  • Pooled SMRs were not significantly increased for amosite (1.14, 95% CI 0.53–2.47, p = 0.73) or crocidolite (1.20, 95% CI 0.70–2.05, p = 0.51).
  • Studies with follow-up of no more than 10 years had a pooled SMR of 1.38 (95% CI 0.86–2.21, p = 0.19), which was not significant. The four longer follow-up subgroups were significantly increased: 1.31 (1.10–1.55), 1.46 (1.20–1.77), 1.22 (1.08–1.37) and 1.25 (1.06–1.47).
  • Industry subgroups: the textile industry pooled SMR was 1.45 (95% CI 1.13–1.86) and the shipyard pooled SMR was 1.39 (95% CI 1.15–1.68); both were significantly increased. Miners: 1.07 (95% CI 0.81–1.41, p = 0.62), not a significant increase.
  • By sex: the pooled SMR for females was 1.61 (95% CI 1.07–2.42, p = 0.02) and for males 1.37 (95% CI 1.21–1.55, p less than 0.00001).
  • Highest asbestos exposure groups in eight studies: pooled SMR 1.84 (95% CI 1.27–2.68, p = 0.001).
  • The risk-of-bias assessment (RoBANS) rated bias from confounding as high in all included studies because potential confounders were not adjusted for.
• The authors' conclusion: The authors concluded that occupational or environmental asbestos exposure might significantly increase the risk of esophageal cancer. They found chrysotile ("chrysolite") significantly associated with esophageal cancer. Citing the long latency period, they suggested that people with a history of asbestos exposure continue follow-up cancer screening for more than ten years.
• Limitations the authors state:
  • The SMRs may be affected by attrition bias. For example, some workers were employed for less than one year, which the authors linked to a healthy worker effect.
  • Only studies reporting SMRs or observed and expected numbers were pooled. Other designs, such as case-control studies, were not included, which may introduce selection bias.
  • Esophageal cancer is affected by multiple factors. The authors said that adjusting for possible confounders such as smoking or alcohol consumption would give more rigorous evidence and is a direction for future research.

Topics

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

Medical terms in this study, explained in our Lexicon: Meta-Analysis, Asbestos Exposure, Esophageal Cancer, confidence interval, Latency.

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