A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers

Our plain-English summary of A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers, by E. Garshick, M.B. Schenker, A. Muñoz, et al (The American Review of Respiratory Disease, 1988).

The study

• Authors: E. Garshick, M.B. Schenker, A. Muñoz, M. Segal, T.J. Smith, S.R. Woskie, S.K. Hammond, F.E. Speizer
• Journal: The American Review of Respiratory Disease
• Published: 1988;137(4):820-5
• Cited by: 125 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000906).

Abstract

The risk of lung cancer as a result of exposure to diesel exhaust from railroad locomotives was assessed in a cohort of 55,407 white male railroad workers 40 to 64 yr of age in 1959 who had started railroad service 10 to 20 years earlier. The cohort was traced until the end of 1980, and death certificates were obtained for 88% of 19,396 deaths; 1,694 lung cancer cases were identified. Yearly railroad job from 1959 to death or retirement was available from the Railroad Retirement Board, and served as an index of diesel exhaust exposure. Directly standardized rates and a proportional hazards model were used to calculate the relative risk of lung cancer based on work in a job with diesel exhaust exposure beginning in 1959. A relative risk of 1.45 (95% CI = 1.11, 1.89) for lung cancer was obtained in the group of workers 40 to 44 yr of age in 1959, the group with the longest possible duration of diesel exposure. The cohort was selected to minimize the effect of past railroad asbestos exposure, and analysis with workers with possible asbestos exposure excluded resulted in a similarly elevated risk. Workers with 20 yr or more elapsed since 1959, the effective start of diesel exposure for the cohort, had the highest relative risk. These results taken in conjunction with other reported results support the hypothesis that occupational exposure to diesel exhaust results in a small but significantly elevated risk for lung cancer.

In plain English

This retrospective cohort study followed 55,407 white male U.S. railroad workers aged 40 to 64 in 1959, selected as having started railroad work between 1939 and 1949, although 56 were estimated to have started in 1950. Through the end of 1980, 1,694 deaths were attributed to lung cancer. Yearly job records from the Railroad Retirement Board were used to classify diesel exhaust exposure as yes or no. Train crews and diesel repair shop workers counted as exposed. Clerks, station agents and signal maintainers counted as unexposed. Among workers aged 40 to 44 in 1959, those in diesel-exposed jobs that year had a lung cancer relative risk of 1.45 (95% confidence interval 1.11 to 1.89) compared with unexposed workers. Among those aged 45 to 49, it was 1.33 (95% confidence interval 1.03 to 1.73). Estimates in the older age groups were lower and did not reach statistical significance. When shop workers and hostlers, the groups with possible past asbestos exposure, were left out, the risk stayed elevated. Smoking could not be directly considered. The authors concluded that occupational diesel exhaust exposure is associated with a modest excess risk of lung cancer.

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
• Who was studied: 55,407 white male U.S. railroad workers, employed and aged 40 to 64 in 1959, who were eligible for railroad benefits and were in the selected job codes in 1959. Workers were selected as having started work between 1939 and 1949, though the final cohort included 56 subjects estimated to have started in 1950. They were followed to the end of 1980, during which there were 19,396 deaths.
• Exposure: Diesel exhaust from railroad locomotives, classified as exposed or unexposed from each year's job code between 1959 and death or retirement through 1980. Exposed workers were train crews (engineers, firemen, brakemen, conductors, hostlers) and diesel locomotive repair shop workers (supervisors, machinists, electricians). Unexposed workers were clerks, ticket and station agents, and signal maintainers. Shop workers and hostlers were categorized as having potential past asbestos exposure from steam-era work. No asbestos fiber type is named.
• Main results:
  • 1,694 deaths (8.7% of deaths) were attributed to lung cancer.
  • Workers aged 40 to 44 in 1959 who were in diesel-exposed jobs in 1959 had a relative risk of lung cancer of 1.45 (95% CI 1.11 to 1.89), adjusted for age, compared with unexposed workers. Those aged 45 to 49 in 1959 had a relative risk of 1.33 (95% CI 1.03 to 1.73). Both were statistically significant (p less than 0.05). These were the groups with the longest possible duration of diesel exposure.
  • Risk estimates in the older age groups (50 to 64 in 1959) were lower and did not reach conventional levels of significance.
  • With shop workers and hostlers (the groups with potential past asbestos exposure) excluded, leaving 42,535 workers, the relative risk was 1.57 (95% CI 1.19 to 2.06) for those aged 40 to 44 in 1959. It was 1.34 (95% CI 1.02 to 1.76) for those aged 45 to 49.
  • In the model that included potential asbestos exposure as a yes/no variable, the relative risk estimates for asbestos exposure were all near the null value.
  • When exposure in the year of death and the 4 years before was disregarded, workers with 15 or more years of diesel-exposed work had a relative risk of 1.72 (95% CI 1.27 to 2.33). The relative risk was 1.20 (95% CI 1.01 to 1.44) for 1 to 4 years, 1.24 (95% CI 1.06 to 1.44) for 5 to 9 years, and 1.32 (95% CI 1.13 to 1.56) for 10 to 14 years.
  • When recent exposure was included, no consistent relationship between duration of exposure and lung cancer risk was found.
• The authors' conclusion: The authors concluded that their findings, together with their earlier pilot and case-control studies, lend credence to the conclusion that occupational diesel exhaust exposure is associated with a modest excess risk of lung cancer.
• Limitations the authors state:
  • Because the study was retrospective, cigarette smoking could not be directly considered.
  • Most workers with significant past asbestos exposure were excluded, but some were probably included as diesel-exposed workers in the diesel repair shop, such as machinists. Using the 1959 job code to identify past asbestos exposure could misclassify it.
  • Cause-specific death certificates could not be obtained for about 11% of deaths. The authors noted that counting these as non-cases would tend to reduce the study's ability to detect an effect.
  • Follow-up beyond 20 years was short, making it difficult to examine the effect of years of exposure and latency.
  • The effect of time since first exposure could not be separated from duration of exposure, because exposure in this cohort only began in the 1950s.
  • Years of exposure is an imprecise stand-in for dose.
  • Unmeasured confounding factors may be particularly important for relative risks in the range of 1.5.

Topics

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

Medical terms in this study, explained in our Lexicon: Cohort Study, Lung Cancer, Death Certificate, Relative Risk, Asbestos Exposure, Occupational Exposure.

Related studies

• A case-control study of lung cancer and diesel exhaust exposure in railroad workers — E. Garshick, M.B. Schenker, et al. (1987)
• Workplace exposure to diesel and gasoline engine exhausts and the risk of colorectal cancer in Canadian men — L. Kachuri, P.J. Villeneuve, et al. (2016)
• A case-control study relating railroad worker mortality to diesel exhaust exposure using a threshold regression model — M.L. Lee, G.A. Whitmore, et al. (2009)
• Past exposure to asbestos among active railroad workers — E. Garshick, M.B. Schenker, et al. (1987)
• Mesotheliomas among railroad workers in the United States — T.F. Mancuso (1991)
• Comparison of expert and job-exposure matrix-based retrospective exposure assessment of occupational carcinogens in The Netherlands Cohort Study — N.S. Offermans, R. Vermeulen, et al. (2012)

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