Asbestos and colorectal cancer

Our plain-English summary of Asbestos and colorectal cancer, by W. Weiss (Gastroenterology, 1990).

The study

• Author: W. Weiss
• Journal: Gastroenterology
• Published: 1990;99(3):876-84
• Type of article: Review
• Cited by: 16 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. 003632).

Abstract

Reports in the literature on 21 cohorts of workers exposed to asbestos were reviewed and analyzed to determine whether there is a causal association between asbestos and colorectal cancer. The latest report up to 1988 was used for each cohort. The end point was the standardized morbidity or mortality ratio as the measure of relative risk. Two additional cohorts using mortality as the end point were excluded because the authors failed to use comparable diagnostic methods for the asbestos-exposed populations and controls. The summary standardized morbidity or mortality ratio for all 21 cohorts was 0.97 (P greater than 0.05), and there was no dose-response relationship in the two studies with such data. The evidence does not meet the established criteria for making a judgment that there is a causal relationship between asbestos and colorectal cancer.

In plain English

This article was a review. The author gathered published cohort studies of asbestos-exposed workers, using the latest report up to 1988 for each, and combined their colorectal cancer results to judge whether asbestos causes colorectal cancer. Twenty-one cohorts were analyzed, covering a wide range of jobs and asbestos fiber types. Across all 21 cohorts, the ratio of observed to expected colorectal cancers (the SMR) was 0.97, which was not statistically significant. It was 0.90 in the inception cohorts and 1.14 in the eight cross-sectional cohorts. Four individual cohorts differed significantly from 1.00. Quebec chrysotile miners (0.78) and asbestos workers in England and Wales (0.51) were lower. An amosite factory (1.85) and U.S.-Canadian insulators (1.59) were higher. The two cohorts with dose-response data showed no convincing dose-response relationship. The author concluded that the criteria for causality were not met, calling the association inconsistent, weak, nonspecific and incoherent. The author noted that the cohorts differed in method, that some were small, and that cohorts with elevated risks may be overrepresented in published material.

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 pooled analysis of published cohort studies of asbestos-exposed workers. Observed and expected colorectal cancer cases were summed to give summary standardized mortality or morbidity ratios (SMRs).
• Who was studied: 21 published cohorts of asbestos-exposed workers, using the latest report up to 1988 for each. There were 13 inception cohorts, ranging from 287 to 10,939 workers each, and 8 cross-sectional cohorts reported in 7 studies.
• Exposure: Occupational asbestos exposure that varied across cohorts by type of work and by fiber type, with chrysotile, crocidolite and amosite in different combinations. Jobs included mining, cement and other factories, shipyards, marine engineering and insulation work.
• Main results:
  • Pooled over all 21 cohorts, the colorectal cancer SMR was 0.97, P greater than 0.05 (not statistically significant).
  • The summary SMR for the 13 inception cohorts was 0.90, not statistically significantly different from 1.00.
  • The summary SMR for the eight cross-sectional cohorts was 1.14, P greater than 0.05.
  • Among inception cohorts, the Quebec chrysotile miners had a statistically significantly low SMR of 0.78 (79 observed versus 101.3 expected).
  • Among inception cohorts, the amosite factory workers had a statistically significantly high SMR of 1.85 (22 observed versus 11.9 expected).
  • Among cross-sectional cohorts, the U.S.-Canadian insulators had a statistically significant SMR of 1.59 (54 observed versus 34.0 expected).
  • Among cross-sectional cohorts, all asbestos-exposed workers in England and Wales had a statistically significant SMR of 0.51 (14 observed versus 27.4 expected).
  • In the two inception cohorts with dose data, no convincing dose-response relationship was found. In the Quebec miners, SMRs across low, medium, high and very high dust concentration categories were 0.58, 0.71, 1.00 and 0.99.
  • No relationship was detected between latency period and colorectal cancer risk. Six cohorts with observation beginning less than 20 years after onset of exposure had a summary SMR of 1.03. Seven cohorts with observation beginning 20 or more years after onset had a summary SMR of 0.86.
  • In nine cohorts with at least 10 expected colorectal cancers, lung cancer SMR and colorectal cancer SMR were closely correlated (r = 0.97). A similar correlation (r = 0.92) appeared in eight cohorts between lung cancer SMR and the SMR for other cancers. The author considered misdiagnosis of lung cancer and mesothelioma a more plausible explanation than asbestos acting as a systemic carcinogen.
• The authors' conclusion: The author concluded that the established criteria for judging a causal relationship between asbestos and colorectal cancer were not met.
• Limitations the authors state:
  • The cohorts differed in method, which made comparisons difficult.
  • The validity of the summary SMR used to combine studies is uncertain.
  • Small cohort sizes may have limited the ability to detect an increased risk.
  • Cohorts with elevated risks may be overrepresented in the published literature, because data not showing elevated risk tend to go unreported.
  • Expected numbers were seldom based on local population rates, which the author considered most relevant.
  • Possible confounding by other carcinogens in asbestos workers' environments, such as hydrocarbons in solvents, had not been taken into account.

Topics

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

Medical terms in this study, explained in our Lexicon: Colorectal Cancer, Relative Risk, Dose-response relationship.

Related studies

• The lack of causality between asbestos and colorectal cancer — W. Weiss (1995)
• The Role of Hyperthermic Intraperitoneal Chemotherapy for Non-colorectal Peritoneal Surface Malignancies — M.C. Morris, J.M. Cloyd, et al. (2021)
• Evidence for excess colorectal cancer incidence among asbestos-exposed men in the Beta-Carotene and Retinol Efficacy Trial — O.A. Aliyu, M.R. Cullen, et al. (2005)
• Exposure to asbestos and the risk of colorectal cancer mortality: a systematic review and meta-analysis — K. Kwak, D. Paek, et al. (2019)
• Colorectal cancer in asbestos cement workers in Denmark — E. Raffn, E. Villadsen, et al. (1996)
• Colorectal cancer and asbestos exposure-an overview — Q. Huang, Y.J. Lan (2020)

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