Occupational exposures and squamous cell carcinoma of the oral cavity, pharynx, larynx, and oesophagus: a case-control study in Sweden

Our plain-English summary of Occupational exposures and squamous cell carcinoma of the oral cavity, pharynx, larynx, and oesophagus: a case-control study in Sweden, by P. Gustavsson, R. Jakobsson, H. Johansson, et al (Occupational and Environmental Medicine, 1998).

The study

• Authors: P. Gustavsson, R. Jakobsson, H. Johansson, F. Lewin, S. Norell, L.E. Rutkvist
• Journal: Occupational and Environmental Medicine
• Published: 1998;55(6):393-400
• Cited by: 104 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: This community based case-referent study was initiated to investigate aetiological factors for squamous cell carcinoma of the upper gastrointestinal tract.

Methods: The study was based on all Swedish men aged 40-79 living in two regions of Sweden during 1988-90. Within that base, efforts were made to identify all incident cases of squamous cell carcinoma of the oral cavity, oropharynx and hypopharynx, larynx, and oesophagus. Referents were selected as a stratified (age, region) random sample of the base. The response was 90% among cases and 85% among referents. There were 545 cases and 641 referents in the final study group. The study subjects were interviewed about several lifestyle factors and a life history of occupations and work tasks. The exposure to 17 specific agents were coded by an occupational hygienist. The relative risk (RR) of cancer was calculated by logistic regression, standardising for age, geographical region, and alcohol and tobacco consumption.

Results: Exposure to asbestos was associated with an increased risk of laryngeal cancer, and a dose-response relation was present. The RR was 1.8 (95% confidence interval (95% CI) 1.1 to 3.0) in the highest exposure group. More than eight years of exposure to welding fumes was associated with an increased risk of pharyngeal cancer (RR 2.3 (1.1 to 4.7)), and laryngeal cancer (RR 2.0 (1.0 to 3.7)). There were indications of a dose-response for duration of exposure. Associations were also found for high exposure to polycyclic aromatic hydrocarbons (PAHs) and oesophageal cancer, RR 1.9 (1.1 to 3.2). Exposure to wood dust was associated with a decreased risk of cancer at the studied sites.

Conclusions: Some of the present findings confirm known or suspected associations--such as asbestos and laryngeal cancer. The study indicates that welding may cause an increased risk of pharyngeal as well as laryngeal cancer. The findings corroborate an association between exposure to PAHs and oesophageal cancer.

In plain English

This case-control study examined workplace exposures and squamous cell carcinoma of the mouth, pharynx (throat), larynx (voice box) and oesophagus in Swedish men aged 40 to 79, 1988 to early 1991. It compared 545 men with these cancers and 641 men from the same population. Nurses interviewed the men about their lifetime jobs, and a hygienist unaware of who had cancer estimated exposure to 17 agents, including asbestos (fiber types not named). Results were adjusted for age, region, alcohol and smoking. High asbestos exposure was associated with laryngeal cancer (risk ratio 1.69, 95% confidence interval 1.05 to 2.74). Risk rose with cumulative exposure (p for trend 0.02). Asbestos showed no clear evidence of increased risk at the other sites. Over eight years of welding was linked with pharyngeal and laryngeal cancer, and high PAH exposure with oesophageal cancer. Wood dust was linked with lower risk among current and former smokers, but among never-smokers the estimate was higher, though imprecise (risk ratio 2.27, 95% confidence interval 0.96 to 5.38). The authors concluded their data strongly supported asbestos as a laryngeal cancer risk factor.

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: Community-based case-control (case-referent) study using face-to-face interviews and hygienist-coded lifetime occupational histories; relative risks were estimated by unconditional logistic regression adjusted for age, region, alcohol and smoking
• Who was studied: Men aged 40 to 79, born in Sweden and living in Stockholm county or the southern healthcare region (about 750 000 men), followed from 1 January 1988 to 31 January 1991. The study included 545 cases of squamous cell carcinoma (128 oral cavity, 138 pharynx, 122 oesophagus, 157 larynx) and 641 population referents. The response was 90% among cases and 85% among referents.
• Exposure: Lifetime occupational exposure to 17 agents, estimated by an occupational hygienist who was blinded to case status. The agents included asbestos (fiber types not specified in the article), PAHs, welding fumes, wood dust, general dust and others. A cumulative exposure index was calculated from intensity, probability and duration. 27.6% of referents had ever been exposed to asbestos.
• Main results:
  • Men in the high asbestos exposure group (above the median cumulative dose among exposed referents) had an increased risk of laryngeal cancer: RR 1.69 (95% CI 1.05 to 2.74), based on 34 cases.
  • The authors found no indications of increased risk of oral, pharyngeal or oesophageal cancer after asbestos exposure. Some estimates at these sites were above 1 but had wide confidence intervals, for example RR 1.21 (95% CI 0.67 to 2.17) for low asbestos exposure and oesophageal cancer.
  • Laryngeal cancer risk rose with cumulative asbestos dose. The p for trend was 0.02 when dose class was used as one variable, and p = 0.008 when cumulative dose was used as a continuous variable.
  • In the highest quartile of cumulative asbestos exposure, the fitted laryngeal cancer RR from the trend model was 1.82 (95% CI 1.08 to 3.04). With each quartile analysed separately, the RR in the highest quartile was 1.77 (95% CI 0.94 to 3.31).
  • For laryngeal cancer, the RR was 1.81 for men exposed to asbestos alone, 3.87 for current smokers alone and 4.78 for current smokers exposed to asbestos. The combined figure was close to what an additive model predicts. The interaction term was not statistically significant (0.68, 0.32 to 1.47).
  • More than eight years of exposure to welding fumes was associated with pharyngeal cancer (RR 2.26, 95% CI 1.09 to 4.68) and laryngeal cancer (RR 1.95, 95% CI 1.03 to 3.69). Adjusting for asbestos changed these estimates only marginally.
  • High PAH exposure was associated with oesophageal cancer (RR 1.87, 95% CI 1.11 to 3.16).
  • Wood dust exposure was associated with a reduced risk of cancer at all sites combined (RR 0.62, 95% CI 0.43 to 0.90).
  • The wood dust result differed by smoking status. Head and neck cancer risk was lower among current smokers (RR 0.59, 95% CI 0.36 to 0.97) and ex-smokers (RR 0.39, 95% CI 0.20 to 0.78). Among men who had never smoked, the estimate was higher (RR 2.27, 95% CI 0.96 to 5.38), and that confidence interval includes 1.
• The authors' conclusion: The authors concluded that their data give strong support for asbestos as a risk factor for laryngeal cancer, and that smoking, alcohol, oral hygiene and welding fumes did not explain the finding. They also concluded that welding fumes were associated with pharyngeal and laryngeal cancer, and that the findings corroborate an association between PAHs and oesophageal cancer.
• Limitations the authors state:
  • Exposure was classified from occupational histories, and the intensity estimates were probably imprecise.
  • The interviewing nurses could not be blinded to whether a man was a case or a referent.
  • The data could not be converted into fibre concentrations or fibre-years.
  • The analysis assumed that cancer risk is proportional to cumulative dose, which may not always hold.
  • The study could detect only large risks for rare exposures, so moderate excess risks cannot be excluded.
  • Because the study was community based, average exposure levels tended to be low and few men had very high exposures.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Squamous Cell Carcinoma, Case-Control Study, Relative Risk, Laryngeal Cancer, Dose-response relationship, confidence interval, Pharyngeal Cancer.

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