Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies

Our plain-English summary of Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies, by L. Fortunato, L. Rushton (British Journal of Cancer, 2015).

The study

• Authors: L. Fortunato, L. Rushton
• Journal: British Journal of Cancer
• Published: 2015;112(11):1805-15
• Type of article: Meta-analysis
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: A recent Monographs Working Group of the International Agency for Research on Cancer concluded that there is limited evidence for a causal association between exposure to asbestos and stomach cancer.

Methods: We performed a meta-analysis to quantitatively evaluate this association. Random effects models were used to summarise the relative risks across studies. Sources of heterogeneity were explored through subgroup analyses and meta-regression.

Results: We identified 40 mortality cohort studies from 37 separate papers, and cancer incidence data were extracted for 15 separate cohorts from 14 papers. The overall meta-SMR for stomach cancer for total cohort was 1.15 (95% confidence interval 1.03-1.27), with heterogeneous results across studies. Statistically significant excesses were observed in North America and Australia but not in Europe, and for generic asbestos workers and insulators. Meta-SMRs were larger for cohorts reporting a SMR for lung cancer above 2 and cohort sizes below 1000.

Conclusions: Our results support the conclusion by IARC that exposure to asbestos is associated with a moderate increased risk of stomach cancer.

In plain English

This meta-analysis pooled results from earlier published studies. The authors sought English-language cohort studies, published 1964 to 2010, of workers mainly exposed to asbestos that reported stomach cancer. They pooled 40 cohorts reporting deaths and 15 reporting new cancer cases. For all 55 cohorts, deaths and new cases combined, the pooled risk ratio (meta-SMR) was 1.15 (95% confidence interval 1.03–1.27), with results varying between studies; for the 40 death cohorts alone it was 1.17 (1.03–1.33). For men it was 1.13 (1.02–1.26). For women, the pooled figure for deaths was 0.93 (0.67–1.30). Among men, raised risks were found for North America and Australia combined (1.30, 1.10–1.55), generic asbestos workers (1.41, 1.10–1.82) and insulators (1.27, 1.05–1.53). In men, cohorts with a lung cancer SMR above 2, which the authors used as a stand-in for heavier exposure, had a meta-SMR of 1.46 (1.22–1.77), versus 1.02 (0.91–1.15) for others. Differences by asbestos type were not statistically significant. Included studies were not adjusted for smoking, diet or Helicobacter pylori infection. The authors concluded that their results support IARC's conclusion that asbestos exposure is associated with a moderate increased risk of stomach cancer.

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 of published occupational cohort studies (mortality and cancer incidence), using random- and fixed-effects models, subgroup analyses and meta-regression
• Who was studied: 55 cohorts of asbestos-exposed workers: 40 mortality cohorts from 37 papers and 15 cancer incidence cohorts from 14 papers. Most were from Europe and North America, with others from China, Russia and Australia. Papers were published in English between 1964 and 2010 and were found through Medline and Embase.
• Exposure: Occupational asbestos exposure in cohorts with predominantly asbestos exposure. Occupations included insulators, generic asbestos workers, textile workers, cement workers, miners and others such as shipyard workers. Fiber types listed were chrysotile, amosite, crocidolite, anthophyllite, tremolite-actinolite and mixed exposures.
• Main results:
  • Total cohort (all 55 cohorts, mortality and incidence combined): meta-SMR for stomach cancer 1.15 (95% CI 1.03–1.27), with heterogeneous results across studies
  • Total cohort, mortality only (40 cohorts): meta-SMR 1.17 (95% CI 1.03–1.33)
  • Men, mortality and incidence combined: meta-SMR 1.13 (95% CI 1.02–1.26)
  • Women, mortality: meta-SMR 0.93 (95% CI 0.67–1.30; 13 studies), with homogeneous results
  • Men, by region: meta-SMR 1.30 (95% CI 1.10–1.55) for North America and Australia analysed together. The text calls this group 'the United States and Australia', while Table 3 labels it 'North America + Australia'.
  • Men, by occupation: highest meta-SMR among generic asbestos workers, 1.41 (95% CI 1.10–1.82), followed by insulators, 1.27 (95% CI 1.05–1.53)
  • Men: cohorts reporting a lung cancer SMR above 2.0, used by the authors as a proxy for high exposure rather than a direct measurement, had a meta-SMR of 1.46 (95% CI 1.22–1.77), compared with 1.02 (95% CI 0.91–1.15) for other cohorts
  • Men, highest exposure category in the 11 studies that reported cumulative or duration of exposure: pooled SMR 1.40 (95% CI 0.81–2.40), with large heterogeneity
  • Men: excluding three influential studies gave a meta-SMR of 1.12 (95% CI 1.04–1.20)
  • The association between asbestos type and the stomach cancer meta-SMR was suggestive but not statistically significant
  • There was evidence of publication bias for the total cohort, but not for men or women analysed separately
• The authors' conclusion: The authors concluded that their results support IARC's conclusion that asbestos exposure is associated with a moderate increased risk of stomach cancer
• Limitations the authors state:
  • The SMRs in the included studies were not adjusted for known stomach cancer risk factors such as Helicobacter pylori infection, smoking and diet
  • Some included studies may not have accounted for co-exposures linked to stomach cancer
  • The included studies came mainly from developed areas, especially Europe; studies from other regions such as developing countries may exist in other databases
  • The authors name the lack of publications from parts of Asia, South America and the former Soviet Union as a possible source of publication bias
  • Exposure categories used for dose-response were not comparable across studies, so only the highest category was used

Topics

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

Medical terms in this study, explained in our Lexicon: Stomach Cancer, Occupational Exposure, Meta-Analysis, Relative Risk, confidence interval, Insulator, Lung Cancer, IARC.

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