Occupational exposures and colorectal cancers: a quantitative overview of epidemiological evidence

Our plain-English summary of Occupational exposures and colorectal cancers: a quantitative overview of epidemiological evidence, by E. Oddone, C. Modonesi, G. Gatta (World Journal of Gastroenterology, 2014).

The study

• Authors: E. Oddone, C. Modonesi, G. Gatta
• Journal: World Journal of Gastroenterology
• Published: 2014;20(35):12431-44
• Type of article: Meta-analysis, Review
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

A traditional belief widespread across the biomedical community was that dietary habits and genetic predisposition were the basic factors causing colorectal cancer. In more recent times, however, a growing evidence has shown that other determinants can be very important in increasing (or reducing) incidence of this malignancy. The hypothesis that environmental and occupational risk factors are associated with colorectal cancer is gaining ground, and high risks of colorectal cancer have been reported among workers in some industrial branches. The aim of this study was to investigate the epidemiologic relationship between colorectal cancer and occupational exposures to several industrial activities, by means of a scientific literature review and meta-analysis. This work pointed out increased risks of colorectal cancer for labourers occupied in industries with a wide use of chemical compounds, such as leather (RR = 1.70, 95%CI: 1.24-2.34), basic metals (RR = 1.32, 95%CI: 1.07-1.65), plastic and rubber manufacturing (RR = 1.30, 95%CI: 0.98-1.71 and RR = 1.27, 95%CI: 0.92-1.76, respectively), besides workers in the sector of repair and installation of machinery exposed to asbestos (RR = 1.40, 95%CI: 1.07-1.84). Based on our results, the estimated crude excess risk fraction attributable to occupational exposure ranged from about 11% to about 15%. However, homogeneous pattern of association between colorectal cancer and industrial branches did not emerge from this review.

In plain English

This article was a literature review and meta-analysis, not a new study of workers. The authors pooled 83 papers, published from 1976 to 2012 and found in PubMed and EMBASE, that reported colorectal, colon or rectal cancer risk by industrial branch. Across all branches combined, colorectal cancer risk was slightly and statistically significantly raised (adjusted pooled relative risk 1.12, 95% CI 1.03 to 1.23). For workers in repair and installation of machinery, the pooled relative risk for colorectal cancer was 1.40 (95% CI 1.07 to 1.84). The authors stated this result came entirely from two cohort studies of Italian shipyard workers exposed to asbestos. Raised risks were also reported for tannery and fur workers (1.70, 95% CI 1.24 to 2.34) and basic metals workers (1.32, 95% CI 1.07 to 1.65). Results for the chemical and the rubber and plastics industries were of borderline significance. The overall rectal cancer estimate was not statistically significant. The authors calculated a crude excess risk fraction from occupational exposure of 10.7% to 13.0%. They concluded that occupational exposures broadly appear to be a risk factor, but found no homogeneous pattern across branches. They noted possible residual confounding and differences between the studies.

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: Literature review and meta-analysis of published cohort studies, case-control studies and meta-analyses, pooled with a random-effects model; trim-and-fill adjustment for publication bias
• Who was studied: 83 papers published from 1976 to 2012, identified in PubMed and EMBASE searches up to June 2013. They gave 141 risk estimates: 60 for colorectal, 57 for colon and 24 for rectal cancer. 68 of the papers were cohort studies.
• Exposure: Employment in industrial branches, reclassified by the authors using the UN International Standard Industrial Classification (ISIC rev. 4). Studies of single chemicals not tied to a job or branch were excluded. Asbestos exposure is named for the Italian shipyard workers in the repair and installation of machinery branch.
• Main results:
  • All industrial branches combined, colorectal cancer: crude pooled RR 1.19 (95% CI 1.09-1.33) and trim-and-fill adjusted RR 1.12 (95% CI 1.03-1.23), per Table 2. Both were statistically significant.
  • Repair and installation of machinery (ISIC 33), colorectal cancer: pooled RR 1.40 (95% CI 1.07-1.84). The result came entirely from two cohort studies of Italian shipyard workers exposed to asbestos.
  • Tannery and fur industry workers (ISIC 15), colorectal cancer: RR 1.70 (95% CI 1.24-2.34).
  • Iron and steel (basic metals, ISIC 24) workers, colorectal cancer: RR 1.32 (95% CI 1.07-1.65).
  • Colorectal cancer results were of borderline significance for the chemical industry (ISIC 20; Table 2 RR 1.27, 95% CI 0.92-1.76) and for rubber and plastics (ISIC 22; Table 2 RR 1.3, 95% CI 0.98-1.71).
  • Colon cancer, all branches combined: RR 1.13 (95% CI 1.05-1.23 in the text). Colon cancer risk was statistically significantly raised for brewery workers, steel and metal workers, and repair and installation of machinery workers (Table 3 crude RR 1.75, 95% CI 1.27-2.41).
  • Rectal cancer, all branches combined: increased but not statistically significant (Table 4 RR 1.15, 95% CI 0.99-1.34).
  • Some mining and quarrying (ISIC 08) and agricultural (ISIC 01) occupations showed significant risk deficits for colorectal cancer (Table 2 pooled RR 0.83, 95% CI 0.77-0.89, and 0.86, 95% CI 0.76-0.97).
  • The crude excess risk fraction attributable to occupational exposure considered as a whole was calculated at 10.7% to 13.0%.
  • Risk in men did not significantly differ from risk in women, except for colorectal cancer. There, men had a pooled estimate of borderline significance (Table 5 adjusted RR 1.10, 95% CI 1.00-1.22).
• The authors' conclusion: The authors concluded that occupational exposures, in a broad sense, appear to be a risk factor for colorectal, colon and rectal cancers. They pointed to increased risks in leather, basic metals, and plastic and rubber manufacturing, and among asbestos-exposed workers in repair and installation of machinery. They also stated that no homogeneous pattern of association emerged across industrial branches.
• Limitations the authors state:
  • Not all studies, especially older ones, gave estimates fully adjusted for known risk or protective factors, so residual confounding cannot be excluded.
  • Excluding studies of single substances not tied to a specific industrial branch may be questionable.
  • Marked heterogeneity between studies, which differed in design, exposure assessment, confounder adjustment and geographic area, may have affected the precision of the pooled estimates.
  • Several branch-specific estimates (furniture, machinery, electronic products, food) were based on only one study each.

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: Occupational Exposure, Colorectal Cancer, Habit, Meta-Analysis.

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