Lung cancer incidence in Canadian petroleum workers

Our plain-English summary of Lung cancer incidence in Canadian petroleum workers, by A.R. Schnatter, M.J. Nicolich, R.J. Lewis, et al (Occupational and Environmental Medicine, 2012).

The study

• Authors: A.R. Schnatter, M.J. Nicolich, R.J. Lewis, F.L. Thompson, H.K. Dineen, I. Drummond, D. Dahlman, A.M. Katz, G. Thériault
• Journal: Occupational and Environmental Medicine
• Published: 2012;69(12):877-82
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: This study's purpose was to conduct a more in-depth analysis of the potential association between lung cancer, occupational exposures and smoking using data on cohort members from a Canadian petroleum company and refined statistical analyses.

Methods: Information on various exposures including asbestos and petroleum coke dust, as well as job type and operating segment were collected via manual and computerised company records. We performed life-table analyses, Poisson regression and restricted cubic splines to model exposure-response patterns while controlling for smoking status and age. Model diagnostics included the assessment of dispersion and offset parameters.

Results: These analyses show that lung cancer risk is strongly related to age and smoking, and to a lesser extent to province of last residence. When controlling for these covariates, there is suggestive evidence that maintenance work may also be related to lung cancer risk. Some analyses also indicate that asbestos exposure may be associated with lung cancer risk, although a clear exposure-response trend is not seen. Other exposures, including petroleum coke dust, were not strongly related to lung cancer risk, particularly when expressed as a continuous measure.

Conclusions: These data suggest that maintenance work may be associated with lung cancer incidence, although exposures to the single agents studied did not emerge as strong predictors of lung cancer incidence. Maintenance work may be a surrogate for general exposures to several agents (eg, polycyclic aromatic hydrocarbons, metals, welding fumes, radiation, etc), although these results may be affected by residual confounding due to smoking or other socio-demographic factors.

In plain English

This retrospective study followed 17 216 male employees of a Canadian petroleum company who had worked there at least one year between 1964 and 1994. It found 44 lung cancer cases through 1994. Asbestos and petroleum coke dust exposures were estimated from company exposure records. The article does not name an asbestos fiber type. Overall, the workers had fewer lung cancers than expected (standardised incidence ratio 0.69, 95% CI 0.50 to 0.92). For maintenance workers the ratio was 1.46 (95% CI 0.83 to 2.36). Ratios rose across the three asbestos exposure groups, but there was no clear exposure-response trend and none was statistically significant. After accounting for age and smoking, having ever worked in maintenance had a relative risk of 2.56 (95% CI 1.00 to 6.56) in one model and 6.1 (95% CI 1.0 to 39.2) in another. The authors described both as borderline significant. In several analyses, once maintenance work was in a model, asbestos and coke dust explained nothing more. The authors concluded that maintenance work was the only consistent occupational factor, perhaps standing for several combined exposures. They noted that smoking not fully controlled for may affect this finding.

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: Retrospective cohort study of cancer incidence, using standardised incidence ratios and Poisson regression (including spline models)
• Who was studied: 17 216 male employees of a Canadian petroleum company who worked at least 1 year between 1 January 1964 and 31 December 1994 and were alive on 1 January 1969. Lung cancers were identified through 1994: 44 cases in 263 529 person-years.
• Exposure: Cumulative asbestos exposure (fibres/cc-years) and respirable petroleum coke dust exposure (mg/m3-years), estimated semi-quantitatively from the company's exposure tracking system. Job type (for example maintenance) and operating segment were also studied. No asbestos fiber type is named.
• Main results:
  • Whole cohort: overall lung cancer SIR 0.69 (95% CI 0.50 to 0.92), a decreased risk compared with the general population
  • Maintenance workers: 16 lung cancer cases, SIR 1.46 (95% CI 0.83 to 2.36)
  • Asbestos-exposed workers: SIRs rose steadily across tertiles of asbestos exposure, but none was statistically significant, and the authors saw no clear exposure-response trend
  • Highest asbestos tertile (more than 0.170 fibres/cc-years): 12 cases, SIR 1.53 (95% CI 0.79 to 2.68)
  • Highest petroleum coke dust tertile: SIR over 2, not statistically significant
  • Optimum discrete model, adjusted for age, smoking and province: ever worked in maintenance, RR 2.56 (95% CI 1.00 to 6.56), p=0.05
  • Same model: current smokers had RR 8.76 (95% CI 1.21 to 63.4)
  • In several analyses, when maintenance work was included in a model along with age and smoking, the asbestos and petroleum coke dust terms added no further explanation of lung cancer risk
  • Continuous-exposure models: maintenance work RR 6.1 (95% CI 1.0 to 39.2), borderline statistically significant (p=0.05). The continuous asbestos term was not statistically significant (p=0.09).
  • Spline analysis of continuous cumulative asbestos exposure: the relative risk first decreased, then increased after about 6.5 fibres/cc-years, and exceeded 1 after about 17 fibres/cc-years, with relatively few observations beyond that point. The 95% CIs always included the null value.
• The authors' conclusion: The authors concluded that, apart from age and smoking, the only consistent occupational factor related to lung cancer was employment as a maintenance worker. They suggested maintenance work may be a surrogate for several combined exposures, and that the finding may be affected by residual confounding from smoking.
• Limitations the authors state:
  • 29% of person-years had less than 25 years of follow-up, which may not be enough to detect occupational lung cancer
  • Model diagnostics showed over-dispersion, suggesting possible uncontrolled confounding or measurement error
  • Exposure estimates were semi-quantitative
  • Exposure estimates may underestimate true exposure
  • Smoking information was missing for 32% of employees
  • Results may be affected by residual confounding from smoking
  • Petroleum coke dust exposure, asbestos exposure and maintenance work were collinear, so models including all three gave unstable estimates

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Occupational Exposure, Asbestos Exposure, Confounding.

Related studies

• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• Mortality Update of a Cohort of Canadian Petroleum Workers — A.R. Schnatter, N.C. Wojcik, et al. (2019)
• Updated mortality among diverse operating segments of a petroleum company — R.J. Lewis, A.R. Schnatter, et al. (2000)
• Update of mortality and cancer incidence in the Australian petroleum industry cohort — R.T. Gun, N. Pratt, et al. (2006)
• Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry — R.T. Gun, N.L. Pratt, et al. (2004)
• Kidney cancer and hydrocarbon exposures among petroleum refinery workers — C. Poole, N.A. Dreyer, et al. (1993)

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