Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry

Our plain-English summary of Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry, by R.T. Gun, N.L. Pratt, E.C. Griffith, et al (Occupational and Environmental Medicine, 2004).

The study

• Authors: R.T. Gun, N.L. Pratt, E.C. Griffith, G.G. Adams, J.A. Bisby, K.L. Robinson
• Journal: Occupational and Environmental Medicine
• Published: 2004;61(2):150-6
• Cited by: 42 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry.

Methods: Employees from 1981 to 1996 were traced through the Australian National Death Index and the National Cancer Statistics Clearing House. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate. Total follow up time was 176 598 person-years for males and 10 253 person-years for females.

Results: A total of 692 of the 15 957 male subjects, and 16 of the 1206 female subjects had died by the cut off date, 31 December 1996. In males, the all-cause SMR and the SMRs for all major disease categories were significantly below unity. There was a non-significant increase of the all-cancer SIR (1.04, 95% CI 0.97 to 1.11). There was a significant increase of the incidence of melanoma (SIR 1.54, 95% CI 1.30 to 1.81), bladder cancer (SIR 1.37, 95% CI 1.00 to 1.83), and prostate cancer (SIR 1.19, 95% CI 1.00 to 1.40), and a marginally significant excess of pleural mesothelioma (SIR 1.80, 95% CI 0.90 to 3.22), leukaemia (SIR 1.39, 95%CI 0.91 to 2.02), and multiple myeloma (SIR 1.72, 95% CI 0.96 to 2.84).

Conclusions: Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. The melanoma excess may be the result of early diagnosis. The excess bladder cancer has not been observed previously in this industry and is not readily explained. The divergence between cancer incidence and cancer mortality suggests that the "healthy worker effect" may be related to early reporting of curable cancers, leading to increased likelihood of cure and prolonged mean survival time.

In plain English

This study updated a cohort of Australian petroleum industry employees (the Health Watch programme). It followed 15 957 men and 1206 women to 31 December 1996, comparing their deaths and cancers with national rates. Men's overall death rate was below the general population's (SMR 0.68, 95% CI 0.63 to 0.73). Their overall cancer incidence was not significantly raised (SIR 1.04, 95% CI 0.97 to 1.11). Eleven pleural mesotheliomas occurred in men (SIR 1.80, 95% CI 0.90 to 3.22), an excess the authors described as marginally significant. There were no peritoneal mesotheliomas. Ten of the cases were refinery workers, six of whom were fitters, welders or maintenance workers. Two had probably had significant asbestos exposure before entering the industry. Lung cancer incidence in men was significantly below expected. Melanoma, bladder cancer and prostate cancer incidence were significantly raised in men. The authors concluded that the mesothelioma excess is probably the legacy of past asbestos exposure in the industry. They noted that not all case work histories were detailed enough to judge whether asbestos exposure in the petroleum industry was responsible.

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: Prospective cohort study (update of mortality and cancer incidence follow-up), comparing the cohort with national rates using standardised mortality ratios and standardised incidence ratios
• Who was studied: Employees of Australian Institute of Petroleum member companies, admitted after five years of service, beginning with surveys in 1980–83: 15 957 males and 1206 females, followed to 31 December 1996 (176 598 male and 10 253 female person-years)
• Exposure: Employment in the petroleum industry (refineries, terminals, airports, onshore and offshore production). Total hydrocarbon exposure was ranked into seven categories from job codes. Asbestos exposure was not measured; it was assessed only from the individual work histories of the mesothelioma cases.
• Main results:
  • Men: all-cause mortality was below that of the general population, SMR 0.68 (95% CI 0.63 to 0.73)
  • Men: all-cancer incidence was not significantly raised, SIR 1.04 (95% CI 0.97 to 1.11)
  • Men: pleural mesothelioma incidence was in marginally significant excess, SIR 1.80 (95% CI 0.90 to 3.22)
  • All 11 pleural cancers in men were mesotheliomas; there were no peritoneal mesotheliomas
  • Of the 11 mesothelioma cases, 10 were refinery workers. Six of these were fitters, welders or maintenance workers, and two had probably had significant asbestos exposure before entering the petroleum industry.
  • Work histories of the mesothelioma cases suggested that most asbestos exposures occurred before the 1970s
  • Men: lung cancer incidence was significantly below expected, SIR 0.65 (95% CI 0.51 to 0.82)
  • Only one death from asbestosis was registered in the cohort
  • Men: melanoma incidence was significantly raised, SIR 1.54 (95% CI 1.30 to 1.81)
  • Men: bladder cancer incidence was significantly raised, SIR 1.37 (95% CI 1.00 to 1.83). Prostate cancer incidence was also significantly raised, SIR 1.19 (95% CI 1.00 to 1.40).
  • Men: bladder cancer incidence showed a significant trend with the highest hydrocarbon rank score ever held (p = 0.02)
  • Men: the excess of all leukaemias combined was not statistically significant, SIR 1.39 (95% CI 0.91 to 2.02)
• The authors' conclusion: The authors concluded that the excess of mesothelioma is probably the legacy of past asbestos exposures in the petroleum industry. They also concluded that the low cancer mortality may reflect earlier diagnosis rather than lower cancer incidence.
• Limitations the authors state:
  • Not all mesothelioma cases had work histories detailed enough to judge whether asbestos exposure in the petroleum industry was responsible
  • The hydrocarbon exposure ranking is a crude measure of exposure
  • Some cohort members could not be traced: 1258 males (8%) and 323 females (27%)
  • Leukaemia incidence is probably underestimated, and numbers of individual leukaemia types were too low to fully evaluate a causal association

Topics

Medical terms in this study, explained in our Lexicon: Standardized Incidence Ratio (SIR), Latency, Pleural Mesothelioma, Myeloma, Mesothelioma, Healthy Worker Effect.

Related studies

• Update of mortality and cancer incidence in the Australian petroleum industry cohort — R.T. Gun, N. Pratt, et al. (2006)
• 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)
• Asbestos-related cancers in refinery workers in the Australian petroleum industry — R. Gun, N.L. Pratt, et al. (2006)
• An updated study of mortality among workers at a petroleum manufacturing plant — Y. Honda, E. Delzell, et al. (1995)

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