Mortality and cancer morbidity in a cohort of Canadian petroleum workers

Our plain-English summary of Mortality and cancer morbidity in a cohort of Canadian petroleum workers, by R.J. Lewis, A.R. Schnatter, I. Drummond, et al (Occupational and Environmental Medicine, 2003).

The study

• Authors: R.J. Lewis, A.R. Schnatter, I. Drummond, N. Murray, F.S. Thompson, A.M. Katz, G. Jorgensen, M.J. Nicolich, D. Dahlman, G. Thériault
• Journal: Occupational and Environmental Medicine
• Published: 2003;60(12):918-28
• Cited by: 63 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To assess mortality and cancer morbidity in Canadian petroleum workers and explore exposure-response relations for specific petroleum agents.

Methods: A total of 25 292 employees hired between 1964 and 1994 were linked to the Canadian tumour registry and national mortality database. Exposure-response trends were assessed for hydrocarbon solvents/fuels, hydrocarbon lubricants, petroleum coke/spent catalyst, and hydrogen sulphide (H2S).

Results: External comparison analyses (mortality and incidence) showed deficits for all causes and all malignant neoplasms combined and were consistent with expectation for most malignant and non-malignant sites analysed. Gall bladder cancer mortality was increased among males based on four deaths, but cases had no common job assignments and the increase was focused in workers employed <10 years. Mesothelioma incidence was increased. Most exposure-specific analyses were compromised by small numbers. Statistically significant increases were observed for H2S exposure and a subgroup of accidental deaths as well as for petroleum coke/spent catalyst exposure and lung cancer. While both findings have a degree of biologic plausibility, the H2S association, which exhibited a clearer exposure-response pattern, could be subject to unmeasured confounders. Additionally, interpretation was complicated by the high correlation between hydrocarbon and H2S exposures. With regard to lung cancer, the analysis could not adequately control for smoking, was based on small numbers, and exhibited a tenuous exposure-response pattern.

Conclusion: The findings for mesothelioma suggest the need for continued attention to asbestos in the petroleum industry. The relation between accidental deaths and H2S exposure deserves closer scrutiny in similarly exposed populations. Further analyses of lung cancer are underway and will be reported separately.

In plain English

This retrospective cohort study followed 25 292 employees of a Canadian petroleum company who were first hired between 1964 and 1994 and worked at least one year. Their records were linked to national death and cancer registry data and compared with the general Canadian population. The authors also estimated exposure to hydrocarbon solvents/fuels, hydrocarbon lubricants, petroleum coke/spent catalyst and hydrogen sulphide. Deaths from all causes were lower than expected for both males and females. Among males, gall bladder cancer deaths were raised (SMR 4.3; 95% CI 1.2 to 11.0), based on four cases. Four mesothelioma cases were found among males against 1.32 expected, and two of them were long-term workers with potential asbestos exposure. Lung cancer was raised among males in the highest petroleum coke/spent catalyst exposure group (RR 3.3; 95% CI 1.4 to 7.7), without a clear exposure-response trend. The authors concluded that the mesothelioma findings suggest the need for continued attention to asbestos in the petroleum industry. They noted low statistical power and missing smoking data, and said they had no information on asbestos exposure before employment.

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 (inception cohort from 1964) linking employees to the Canadian cancer registry and national mortality database, with comparison to general Canadian population rates and exposure-response analyses for four petroleum agents
• Who was studied: 25 292 employees (17 230 males, 8 062 females) of a Canadian petroleum company, first hired from 1 January 1964 to 31 December 1994, with at least one year of employment
• Exposure: Semi-quantitative estimated cumulative exposure to hydrocarbon solvents/fuels, hydrocarbon lubricants, petroleum coke/spent catalyst, and hydrogen sulphide. Asbestos exposure was not measured; it was considered only through work histories of the mesothelioma cases.
• Main results:
  • Deaths from all causes and from all malignant neoplasms were lower than expected for both males and females. For all causes, males had 462 observed versus 711.86 expected deaths (SMR 0.65; 95% CI 0.59 to 0.71) and females had 109 versus 158.91 (SMR 0.69; 95% CI 0.56 to 0.83).
  • Gall bladder cancer mortality was the only statistically significant increase, among males: SMR 4.3 (95% CI 1.2 to 11.0), based on four cases.
  • Four mesothelioma cases were identified among males versus 1.32 expected (cancer incidence).
  • Of the four male mesothelioma cases, two were long-term workers with potential asbestos exposure.
  • Only one death from mesothelioma was observed versus 1.3 expected.
  • Lung cancer incidence among all males was lower than expected: 44 observed versus 63.98 expected (SIR 0.69; 95% CI 0.50 to 0.92).
  • Among males, lung cancer risk was statistically significantly increased in the highest petroleum coke/spent catalyst exposure group (RR 3.3; 95% CI 1.4 to 7.7, 7 cases), with no clear exposure-response trend.
  • Among males, transportation accident deaths showed an exposure-response trend with cumulative hydrogen sulphide exposure. Risk was statistically significant in the highest category (RR 2.3; 95% CI 1.2 to 4.4).
• The authors' conclusion: The authors concluded that, because the cohort included only employees hired in 1964 or later, the mesothelioma findings suggest the need for continued attention to asbestos in the petroleum industry. Overall, they described a favourable health profile.
• Limitations the authors state:
  • The cohort was young, with few deaths and few incident tumours, so statistical power was limited.
  • Smoking status was known for only 43% of the cohort, preventing adequate control for smoking.
  • There were no data on asbestos exposure before employment with the company, and the number of mesothelioma cases was small.
  • The large number of comparisons made increases the likelihood of chance findings.
  • Case identification by the tumour registry may have been incomplete in early years and in Quebec before 1977.

Topics

Medical terms in this study, explained in our Lexicon: Cancer Registry, Neoplasm, Mesothelioma, Lung Cancer.

Related studies

• 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)
• Lung cancer incidence in Canadian petroleum workers — A.R. Schnatter, M.J. Nicolich, et al. (2012)
• Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry — R.T. Gun, N.L. Pratt, et al. (2004)
• An updated mortality study of workers at a petroleum refinery in Beaumont, Texas — G.K. Raabe, K.W. Collingwood, et al. (1998)

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