Colorectal cancer and asbestos exposure-an overview

Our plain-English summary of Colorectal cancer and asbestos exposure-an overview, by Q. Huang, Y.J. Lan (Industrial Health, 2020).

The study

• Authors: Q. Huang, Y.J. Lan
• Journal: Industrial Health
• Published: 2020;58(3):200-211
• Type of article: Meta-analysis
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The relationship between colorectal cancer and asbestos exposure has not been fully clarified. This study aimed to determine the associations between asbestos exposure and colorectal cancer. We performed a meta-analysis to quantitatively evaluate this association. A fixed effects model was used to summarize the relative risks across studies. Sources of heterogeneity were explored through subgroup analyses and meta-regression. We analyzed the dose-effect relationship using lung cancer standardized mortality ratio (SMR) and the risk of mesothelioma as a percent (%) as exposure surrogates. A total of 47 cohort studies were included. We identified 28 incidence cohort studies from 17 separate papers and extracted colorectal cancer standardized incidence ratio (SIR). Cancer mortality data were extracted from 19 separate cohorts among 13 papers. The overall colorectal cancer SMR for synthesis cohort was 1.07 (95% CI 1.02-1.12). Statistically significant excesses were observed in exposure to mixed asbestos (SMR/SIR=1.07), exposure to production (SMR/SIR=1.11), among asbestos cement workers (SMR/SIR=1.18) and asbestos textile workers (SMR/SIR=1.11). Additionally, we determined that the SMR for lung cancer increased with increased exposure to asbestos, as did the risk for colorectal cancer. This study confirms that colorectal cancer has a positive weak associations with asbestos exposure.

In plain English

This review and meta-analysis pooled earlier cohort studies of asbestos-exposed people to look at colorectal cancer. The authors included 47 cohorts from 30 papers found in literature searched up to July 2017. Of these, 19 reported deaths and 28 reported new cancer cases. Across all cohorts, the combined ratio of observed to expected colorectal cancer (SMR/SIR) was 1.07 (95% CI 1.02-1.12). It was 1.18 for asbestos cement workers, 1.11 for asbestos textile workers, 1.11 (95% CI 1.02-1.21) for production exposure and 1.07 (95% CI 1.02-1.13) for mixed asbestos. Serpentine asbestos gave 0.96 (95% CI 0.80-1.15) and amphibole 1.18 (95% CI 0.99-1.41), neither statistically significant. Where reported, the authors used a cohort's lung cancer SMR as a sign of exposure level. Cohorts with a lung cancer SMR of 2 or more had a colorectal ratio of 1.32 (95% CI 1.19-1.46), against 1.01 (95% CI 0.96-1.07) below 2. Mesothelioma risk as the exposure measure showed no dose-effect trend. The authors concluded that colorectal cancer has a positive weak association with asbestos exposure. They noted that incomplete cohort data prevented a fuller dose-effect analysis.

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 with meta-analysis of published cohort studies, using a fixed effects model, subgroup analyses and meta-regression
• Who was studied: 47 cohorts from 30 papers, found in literature retrieved before July 2017. Mortality data came from 19 cohorts in 13 papers and incidence data from 28 cohorts in 17 papers. Cohorts ranged from 167 to 31,150 people and were in Europe, America and Oceania.
• Exposure: Asbestos exposure, grouped by asbestos type (serpentine, amphibole, mixed), by occupation (asbestos cement workers, asbestos textile workers, miners and millers, and repair welding and insulation workers in shipbuilding, railway and workshop), and by exposure way (production, application, living, mixed). Lung cancer SMR, where reported, and mesothelioma risk (%) were used as stand-ins for exposure level.
• Main results:
  • Combined colorectal cancer SMR/SIR across all 47 cohorts: 1.07 (95% CI 1.02-1.12)
  • By occupation: asbestos cement workers had an SMR/SIR of 1.18 and asbestos textile workers 1.11, both reported as statistically significant. Asbestos miners and millers had 0.93, and repair welding and insulation workers 1.06. No confidence intervals are given for the occupation subgroups.
  • By exposure way: production 1.11 (95% CI 1.02-1.21, statistically significant), application 1.06 (95% CI 0.99-1.12), living 1.34 (95% CI 0.99-1.81), and mixed sources 1.00 (95% CI 0.89-1.14)
  • By asbestos type: serpentine 0.96 (95% CI 0.80-1.15) and amphibole 1.18 (95% CI 0.99-1.41), neither statistically significant. Mixed asbestos 1.07 (95% CI 1.02-1.13), statistically significant.
  • Colorectal SMR/SIR was 1.01 (95% CI 0.96-1.07) in cohorts with a lung cancer SMR below 2, and 1.32 (95% CI 1.19-1.46) in cohorts with a lung cancer SMR of 2 or more. Nine incidence cohorts did not report a lung cancer SMR.
  • By follow-up period: less than 35 years 1.04 (95% CI 0.96-1.13), and 35 years or more 1.09 (95% CI 1.03-1.15)
  • When the lung cancer SMR was above 2.88, the colorectal cancer SMR showed a gentle increasing trend
  • With mesothelioma risk (%) as the exposure measure, no dose-effect trend was seen
  • For comparison, gastric cancer in the same cohorts had an overall SMR/SIR of 1.04 (95% CI 0.98-1.10), which was not statistically significant
• The authors' conclusion: The authors concluded that colorectal cancer has a positive weak association with asbestos exposure. They also concluded that mixed asbestos exposure, and production work such as asbestos cement and textile work, show a weak correlation with colorectal cancer risk.
• Limitations the authors state:
  • Imperfect cohort data meant the dose-effect relationship could not be worked out more fully
  • Meta-analysis has inherent defects, such as publication bias and simplification
  • The living (environmental) exposure subgroup had only 2 cases, so its result should be used cautiously

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, Asbestos Exposure, Meta-Analysis, Relative Risk, Lung Cancer, standardized mortality ratio (SMR), Mesothelioma, Standardized Incidence Ratio (SIR).

Related studies

• Occupational exposures and colorectal cancers: a quantitative overview of epidemiological evidence — E. Oddone, C. Modonesi, et al. (2014)
• Colorectal cancer in asbestos cement workers in Denmark — E. Raffn, E. Villadsen, et al. (1996)
• 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)
• The lack of causality between asbestos and colorectal cancer — W. Weiss (1995)
• Exposure to asbestos and the risk of colorectal cancer mortality: a systematic review and meta-analysis — K. Kwak, D. Paek, et al. (2019)
• Asbestos and colorectal cancer — W. Weiss (1990)

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