Asbestos exposure and gastrointestinal malignancy review and meta-analysis

Our plain-English summary of Asbestos exposure and gastrointestinal malignancy review and meta-analysis, by H. Frumkin, J. Berlin (American Journal of Industrial Medicine, 1988).

The study

• Authors: H. Frumkin, J. Berlin
• Journal: American Journal of Industrial Medicine
• Published: 1988;14(1):79-95
• Type of article: Review
• Cited by: 77 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000220).

Abstract

The epidemiologic literature linking asbestos exposure with gastrointestinal malignancy is reviewed. Problems in comparing studies are discussed, appropriate strategies for comparison are developed, and study results are pooled using a model which accounts for both intrastudy and interstudy variability. Stratification of cohorts by dose reveals that significant asbestos exposure, as indicated by a lung cancer standardized mortality ratio (SMR) of at least 200, is associated with an elevated gastrointestinal cancer of SMR for five of six points examined [corrected].

In plain English

This article was a review and meta-analysis of published English-language mortality studies of asbestos-exposed worker cohorts. The cohorts included cement workers, insulators, miners and millers, textile workers, shipyard workers and other industrial workers. Few studies measured exposure, so the authors used each cohort's lung cancer standardized mortality ratio (SMR) as a stand-in for asbestos dose. The SMR compares observed deaths with expected deaths, with 100 meaning no excess. They pooled results with a statistical model that allowed for differences between studies. In cohorts with a lung cancer SMR above 200, pooled SMRs were raised, with 95% confidence intervals excluding 100, for five of six digestive-tract end points. Examples were 134 (107-167) for stomach cancer and 161 (134-193) for colorectal cancer. Esophageal cancer was the exception, at 95 (26-347). In cohorts with lower lung cancer SMRs, all pooled SMRs were close to 100. Splitting the data by fiber type or industry left too little data to be informative. The authors concluded that gastrointestinal cancer SMRs were quite consistently elevated among cohorts with significant asbestos exposure. They noted that the confidence intervals for stomach and esophageal cancer were less reliable than those for colorectal and total gastrointestinal 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: Review and meta-analysis of published cohort mortality studies, pooled with a random-effects model that accounts for variability within and between studies
• Who was studied: Cohort studies of asbestos workers published in English that used mortality as an end point and gave observed and expected counts for gastrointestinal cancers. Groups were cement workers, insulators, miners and millers, textile workers, shipyard workers and other industrial workers from several countries. Only the most recent report on each cohort was used.
• Exposure: Occupational asbestos exposure across different industries and fiber types (chrysotile, amosite, mixed and others). Dose was represented by each cohort's lung cancer SMR. Cut-points of 150, 200 and 250 were considered, and results were reported for lung cancer SMR below versus above 200.
• Main results:
  • In high-exposure cohorts (lung cancer SMR above 200), pooled SMRs for all end points except esophagus were elevated, with 95% confidence intervals excluding 100. In low-exposure cohorts, all SMRs were close to 100.
  • Gastric cancer, cohorts with lung cancer SMR above 200 (all cohorts, 6 pooled): pooled SMR 134 (95% CI 107-167)
  • Colorectal cancer, cohorts with lung cancer SMR above 200 (6 cohorts): pooled SMR 161 (95% CI 134-193)
  • Esophageal cancer, cohorts with lung cancer SMR above 200 (5 cohorts): pooled SMR 95 (95% CI 26-347)
  • Gastrointestinal tract cancer (ICD 150-154), cohorts with lung cancer SMR above 200 (3 cohorts): pooled SMR 200 (95% CI 138-289)
  • All gastrointestinal cancer apparently including mesothelioma, cohorts with lung cancer SMR above 200 (6 cohorts): pooled SMR 153 (95% CI 109-217)
  • Among high-exposure cohorts in studies that took latency into account, the point estimates were 147 for esophageal cancer, 146 for gastric cancer and 168 for colorectal cancer.
  • For all gastrointestinal cancer with mesothelioma counted separately, a significant SMR elevation appeared only when latency was considered.
  • Differences between studies were large before stratification. After stratifying on lung cancer SMR, the hypothesis that the studies agreed generally was not rejected.
  • Mortality from causes considered unrelated to asbestos was 99 (95% CI 93-107) in 9 cohorts with lung cancer SMR below 200, and 119 (95% CI 111-128) in 12 cohorts above 200. The authors described this as a slight, though significant, difference.
  • The authors examined the argument that gastrointestinal cancer excesses come from misdiagnosed lung cancers and mesotheliomas. Based on studies that re-reviewed death certificate diagnoses, they found no available evidence supporting this for gastrointestinal cancer.
• The authors' conclusion: The authors concluded that gastrointestinal cancer SMRs were quite consistently elevated among cohorts with significant asbestos exposure, as shown by raised lung cancer SMRs. They judged these patterns likely to reflect a biological effect of asbestos rather than an artifact of study design. They considered the question of a systemic carcinogenic effect still open.
• Limitations the authors state:
  • The methods rely on large-sample theory, so the confidence intervals for gastric and esophageal cancer are less valid than those for colorectal and total gastrointestinal cancer.
  • The test for differences between studies is likely not very powerful, especially when few studies are pooled.
  • Differences in age structure between cohorts could not be corrected without age- or latency-specific data.
  • Differences in how closely exposed workers were diagnosed, compared with the general population, could not be measured.
  • Stratifying by fiber type and industry gave tables too sparse to be informative.
  • Using lung cancer SMR as an exposure measure would be invalid if lung cancer elevations came from better death ascertainment, low-mortality comparison groups or other systematic bias.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Meta-Analysis, Lung Cancer, standardized mortality ratio (SMR).

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