Risk of gastrointestinal cancers from inhalation and ingestion of asbestos

Our plain-English summary of Risk of gastrointestinal cancers from inhalation and ingestion of asbestos, by J. Gamble (Regulatory Toxicology and Pharmacology, 2008).

The study

• Author: J. Gamble
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S124-53
• Type of article: Review
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This paper summarizes the weight of epidemiological evidence to evaluate the hypothesis that asbestos exposure is causally associated with increased risk of gastrointestinal (GI) cancers as suggested by Selikoff in an early study of insulation workers. This review looks at populations that develop GI cancers, namely stomach, colorectal, colon and rectal. Guidelines for assessing causality are strength of association, biological gradient and consistency of the associations. Exposure-response (E-R) was evaluated using three methods to estimate exposure. Rate Ratios (RRs) for lung cancer and percent of mesothelioma are used as surrogate measures of asbestos exposure for all the cohorts of exposed workers. Quantitative or semi-quantitative estimates of cumulative exposure to asbestos were also used to assess E-R trends and were compared to E-R trends for lung cancer and mesothelioma in individual studies. Surrogate measures are important since there are few individual studies that have assessed E-R. None of the various methods to estimate asbestos exposure yielded consistent E-R trends and the strength of the associations were consistently weak or non-existent for the four types of GI cancers. The epidemiological evidence detracts from the hypothesis that occupational asbestos exposure increases the risk of stomach, colorectal, colon, and rectal cancer. Findings are briefly summarized below.

In plain English

This was a review weighing whether asbestos exposure is causally linked to stomach, colorectal, colon and rectal cancer. The author searched Toxline and Medline and summarized 44 worker studies. Because relatively few studies had analyzed these cancers against individual exposure, the author also used each group's lung cancer risk and percent mesothelioma as rough stand-ins for exposure. Across studies, the combined risk ratio was 1.01 (0.94–1.08) for stomach cancer (37 cohorts, 791 cases), 0.97 (0.89–1.05) for colorectal cancer (22 studies, 599 cases), 0.96 (0.87–1.07) for colon cancer (16 cohorts, 365 cases) and 1.06 (0.94–1.19) for rectal cancer (15 cohorts, 291 cases). When the studies with lung cancer risk above 3-fold were pooled, the risk ratio was 1.43 (1.08–1.88) for stomach cancer and 1.60 (1.29–2.0) for colorectal cancer. Exceptions included a 3-fold stomach cancer excess above 1000 mppcf-years among Canadian chrysotile miners and millers. The author described the drinking-water data as few and weak. The author concluded the evidence detracts from the hypothesis that occupational asbestos exposure increases risk of these cancers.

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 (weight-of-evidence review of published cohort and case-control studies of asbestos-exposed workers, plus ecological and other studies of asbestos in drinking water)
• Who was studied: 44 published studies of asbestos-exposed workers, including chrysotile miners/millers and asbestos cement, factory, textile, shipyard and maintenance workers in several countries. Drinking-water studies from Duluth, Minnesota, other US areas, Quebec and Norwegian lighthouse keepers were also reviewed.
• Exposure: Occupational asbestos exposure, with fiber types varying by study (chrysotile, amosite, crocidolite, anthophyllite, tremolite-contaminated vermiculite). Exposure was estimated three ways: lung cancer risk ratios as a stand-in for exposure, percent mesothelioma as a stand-in for exposure, and quantitative or semi-quantitative cumulative exposure where individual studies gave it. Ingestion of asbestos in drinking water was also reviewed. Fiber type was not analyzed.
• Main results:
  • Stomach cancer: 37 cohorts with 791 cases, overall risk ratio 1.01 (0.94–1.08)
  • Colorectal cancer: 22 studies with 599 cases, overall SMR 0.97 (0.89–1.05)
  • Colon cancer: 16 cohorts with 365 cases, SMR 0.96 (0.87–1.07)
  • Rectal cancer: 15 cohorts with 291 cases, overall SMR 1.06 (0.94–1.19)
  • Pooled stomach cancer SMR in the subgroup of studies with lung cancer SMRs above 3.0: 1.43 (1.08–1.88)
  • Pooled colorectal cancer SMR in the subgroup of studies with lung cancer risk ratios above 3: 1.60 (1.29–2.0)
  • Exception: among Canadian chrysotile miners/millers, stomach cancer and lung cancer risk were significantly increased 3-fold at cumulative exposures above 1000 mppcf-years
  • Exception: in Albin et al. (1990), Swedish asbestos cement workers had a significant 3-fold colorectal cancer relative risk at about 40 f/ml-years
  • Drinking-water (ingestion) studies showed no association with GI cancers, but the author described the data as few and weak
• The authors' conclusion: The author concluded that the epidemiological evidence detracts from the hypothesis that occupational asbestos exposure increases the risk of stomach, colorectal, colon and rectal cancer.
• Limitations the authors state:
  • Comparisons with outside populations could only be adjusted for age, sex and race, so some bias and confounding was unavoidable
  • Lung cancer as a stand-in for exposure is affected by smoking, which varies between cohorts
  • Individual-level exposure-response data cover only a fraction of the total cases
  • GI cancers were often not the main interest of the original studies and were sometimes combined
  • Analysis by fiber type was not done

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Insulator, rate ratio, Lung Cancer, Mesothelioma, Cumulative Exposure.

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