Occupational exposures to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx: a quantitative literature review

Our plain-English summary of Occupational exposures to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx: a quantitative literature review, by S. Paget-Bailly, D. Cyr, D. Luce (International Archives of Occupational and Environmental Health, 2012).

The study

• Authors: S. Paget-Bailly, D. Cyr, D. Luce
• Journal: International Archives of Occupational and Environmental Health
• Published: 2012;85(4):341-51
• Type of article: Meta-analysis, Review
• Cited by: 44 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: The role of occupational risk factors in oral and pharyngeal cancer is not well known and is possibly underestimated. This quantitative review summarizes epidemiological findings on exposure to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx.

Methods: A systematic literature search was performed. We analyzed 63 publications: 8 from case-control studies and 55 from cohort studies. For agents with at least five available studies with homogenous exposure, a series of meta-analyses was conducted to provide quantitative pooled estimates of risks, using random effect models.

Results: Exposure to asbestos (meta-RR 1.25; 95% CI 1.10-1.42) and to polycyclic aromatic hydrocarbons (meta-RR 1.14; 95% CI 1.02-1.28) was found to be associated with oral and pharyngeal cancer risk. On the other hand, no association was found with exposure to solvents in general (meta-RR 0.98; 95% CI 0.77-1.23) but the strong heterogeneity between studies suggested differences in exposures. The small number of studies with homogeneous exposure did not allow meta-analyses for specific solvents.

Conclusions: Future investigations should overcome common weaknesses of past studies, in terms of sample size, characterization of exposure, and classification of cancer sites.

In plain English

This article was a literature review with meta-analyses. The authors reviewed studies published from 1980 to 2010 on workplace exposure to asbestos, polycyclic aromatic hydrocarbons (PAHs) and solvents and oral cavity and pharynx cancers. They analyzed 63 publications: 8 case–control studies and 55 cohort or record linkage studies. Pooling 23 cohort studies of asbestos-exposed workers, they found a combined relative risk of 1.25 (95% CI 1.10–1.42) for oral cavity and pharynx cancer together. By type of work, it was 1.63 (1.27–2.09) for miners and millers, 0.91 (0.70–1.18) for construction workers, 1.41 (0.97–2.07) for asbestos textile workers and 1.13 (0.56–2.25) for asbestos-cement workers. The pooled figure for PAHs was 1.14 (1.02–1.28). For solvents in general it was 1.00 (0.73–1.35) or 0.98 (0.77–1.23), depending on which exposure level was taken from one case–control study; results varied between solvent studies. The authors called this suggestive evidence of an association for asbestos and PAHs. They noted that cohort studies usually lacked smoking and alcohol data and that many studies were small. They also noted that dose–response could not be assessed, which ruled out firm conclusions about causation.

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: Systematic literature review with random-effects meta-analyses of published case–control, cohort and record linkage studies
• Who was studied: 63 publications found through a PubMed search and reference lists: 8 case–control studies and 55 cohort and record linkage studies, published between 1980 and 2010 in French and English
• Exposure: Occupational exposure to asbestos (pooled studies of miners and millers, construction workers, asbestos textile workers, asbestos-cement workers and other asbestos-exposed groups), polycyclic aromatic hydrocarbons, and solvents. Outcomes were cancers of the oral cavity, oropharynx and hypopharynx, or pharyngeal cancer as a whole when subsite data were unavailable.
• Main results:
  • Asbestos, 23 cohort studies: the pooled relative risk (meta-RR) for cancer of the oral cavity and pharynx grouped together was 1.25 (95% CI 1.10–1.42)
  • Asbestos, by exposure circumstance: meta-RR 1.63 (95% CI 1.27–2.09) for miners and millers and 0.91 (95% CI 0.70–1.18) for construction workers
  • Asbestos, by exposure circumstance: meta-RR 1.41 (95% CI 0.97–2.07) for asbestos textile workers and 1.13 (95% CI 0.56–2.25) for asbestos-cement workers
  • Asbestos and pharyngeal cancer: the high exposure meta-RR was 1.27 (95% CI 0.98–1.66), based on 3 case–control and 5 cohort studies
  • Asbestos and oral cavity cancer: the high exposure meta-RR was 1.15 (95% CI 0.84–1.57) and the low exposure meta-RR was 1.13 (95% CI 0.81–1.57)
  • An association between asbestos and hypopharyngeal cancer suggested in case–control studies could not be confirmed in cohort studies, because those studies lacked data on cancer subsites
  • PAHs, 22 cohort studies: meta-RR 1.14 (95% CI 1.02–1.28) for oral cavity and pharynx cancer together
  • Solvents in general, using the high cumulative exposure result from one case–control study: meta-RR 1.00 (95% CI 0.73–1.35) for oral cavity and pharynx cancer together, with strong heterogeneity between studies
  • Solvents in general, using the low cumulative exposure result instead: meta-RR 0.98 (95% CI 0.77–1.23) for oral cavity and pharynx cancer together
  • The authors found no evidence of publication bias
• The authors' conclusion: The authors concluded that their results provide suggestive evidence of an association of asbestos and PAHs with cancer of the oral cavity or pharynx, and that the possible role of these agents needs further investigation
• Limitations the authors state:
  • Cohort studies typically lacked data on smoking and alcohol drinking, the major risk factors for these cancers
  • Many studies were small, with limited statistical power to detect moderate increases in risk
  • Cancer sites were defined and grouped inconsistently across studies, which made comparison difficult
  • Exposures were poorly characterized, so dose–response could not be assessed and no firm conclusion about causality was possible
  • Only about 17% of asbestos cohort studies listed in an earlier meta-analysis reported results on oral and pharyngeal cancers
  • Two case–control studies without confidence intervals could not be included, which may have slightly overestimated the meta-RRs
  • Restricting the review to studies published from 1980 onward may have led to a loss of information
  • Results for construction worker cohorts were difficult to interpret because the workers had multiple co-exposures

Topics

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

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Pharyngeal Cancer.

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