Occupational Exposure to Diesel Motor Exhaust and Lung Cancer: A Dose-Response Relationship Hidden by Asbestos Exposure Adjustment? The ICARE Study

Our plain-English summary of Occupational Exposure to Diesel Motor Exhaust and Lung Cancer: A Dose-Response Relationship Hidden by Asbestos Exposure Adjustment? The ICARE Study, by M. Matrat, F. Guida, S. Cénée, et al (Journal of Cancer Epidemiology, 2015).

The study

• Authors: M. Matrat, F. Guida, S. Cénée, J. Févotte, M. Carton, D. Cyr, G. Menvielle, S. Paget-Bailly, L. Radoï, A. Schmaus, S. Bara, M. Velten, D. Luce, I. Stücker, The Icare Study Group
• Journal: Journal of Cancer Epidemiology
• Published: 2015;2015:879302
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background. In a French large population-based case-control study we investigated the dose-response relationship between lung cancer and occupational exposure to diesel motor exhaust (DME), taking into account asbestos exposure. Methods. Exposure to DME was assessed by questionnaire. Asbestos was taken into account through a global indicator of exposure to occupational carcinogens or by a specific JEM. Results. We found a crude dose response relationship with most of the indicators of DME exposure, including with the cumulative exposure index. All results were affected by adjustment for asbestos exposure. The dose response relationships between DME and lung cancer were observed among subjects never exposed to asbestos. Conclusions. Exposure to DME and to asbestos is frequently found among the same subjects, which may explain why dose-response relationships in previous studies that adjusted for asbestos exposure were inconsistent.

In plain English

This French population-based case-control study, called ICARE and run from 2001 to 2007, looked at whether men's work exposure to diesel motor exhaust was linked to lung cancer. It also looked at how taking asbestos exposure into account changed that link. The analysis included 2264 men with lung cancer and 2780 men without it. Diesel exposure was self-reported by questionnaire. Asbestos exposure was estimated from job histories with a job-exposure matrix, in a broader ('sensitive') and a narrower ('specific') version. Men reporting diesel exposure had higher odds of lung cancer (OR 1.3, 95% CI 1.1–1.6), and the odds rose with cumulative exposure. Adjusting for asbestos weakened these associations, most with the sensitive asbestos measure. Among 638 cases and 1147 controls never exposed to asbestos, definite diesel exposure had an OR of 1.46 (95% CI 1.03–2.07), with significant dose-response trends. The authors concluded that diesel exhaust is a lung cancer risk factor not explained by smoking or asbestos. They noted that self-reported exposure means bias cannot be fully excluded.

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: Multicentre population-based case-control study
• Who was studied: 5044 men in France: 2264 lung cancer cases from 10 départements with cancer registries, and 2780 population controls frequency-matched by age, gender and département. Women were excluded from the analysis.
• Exposure: Occupational diesel motor exhaust (DME), assessed for each job period by a single questionnaire question. Asbestos exposure was assessed with an asbestos job-exposure matrix (JEM) in a sensitive and a specific version; the article does not name fiber types. 'List A' jobs (jobs linked to lung cancer) and a silica JEM were also used for adjustment.
• Main results:
  • All men: those who declared definite DME exposure had higher odds of lung cancer, OR 1.3 (95% CI 1.1–1.6). This is adjusted for age, département, smoking index and number of jobs; Table 3 gives 1.35 (1.13–1.61).
  • All men: risk rose with the DME cumulative exposure index. The text gives OR 1.4 (95% CI 1.1–1.6) for the highest class; Table 3 gives 1.36 (1.09–1.70) for the class above 31.
  • All men: the text states no relation with duration of DME exposure was observed.
  • All men: adjusting for asbestos cumulative exposure reduced the DME associations, more so with the sensitive asbestos definition. Table 3 values for definite DME exposure: OR 1.20 (95% CI 1.0–1.44), trend p 0.15 (sensitive); OR 1.26 (95% CI 1.05–1.51), trend p 0.01 (specific). Cumulative exposure index trend: p 0.12 (sensitive); p 0.04 (specific).
  • No effect modification was detected between asbestos exposure (sensitive definition) and DME (p = 0.66).
  • Results by smoking status were rather similar for definite DME exposure: nonsmokers OR 1.37 (95% CI 0.67–2.7), ex-smokers 1.27 (0.98–1.64), current smokers 1.46 (1.1–1.9). No modification effect was detected (p = 0.35).
  • Men never exposed to asbestos (sensitive definition) formed a subgroup of 638 cases and 1147 controls.
  • In this never-exposed subgroup, all DME measures showed significant dose-response relationships. Certain DME exposure: OR 1.46 (95% CI 1.03–2.07). More than 15 years of exposure: OR 1.54 (1.00–2.36), trend p 0.047. Cumulative exposure index above 31: OR 1.62 (1.05–2.51), trend p 0.03.
  • In the never-exposed subgroup, further adjustment for List A or silica still showed a significant increased risk. With silica adjustment, certain DME exposure: OR 1.44 (95% CI 1.01–2.04).
  • In the never-exposed subgroup, after also excluding men with high school or university degrees, the relationship was consistent but not statistically significant. Certain DME exposure: OR 1.31 (95% CI 0.82–2.10).
  • The estimated population attributable fraction of lung cancer due to DME was 7.0% (95% CI 1.3–12.4), based on the never-asbestos-exposed subgroup. For the whole population, adjusting for asbestos (specific definition), it was 7.2% (95% CI 1.8–12.3).
  • Asbestos exposure itself showed a dose-response relationship with lung cancer under both definitions. Highest exposure class: OR 2.3 (95% CI 1.7–3.0) with the sensitive definition and 1.7 (95% CI 1.2–2.3) with the specific definition.
• The authors' conclusion: The authors concluded that their study highlights DME exposure as a lung cancer risk factor that is not due to smoking or asbestos exposure. They suggested that adjusting for asbestos weakens the DME association, which could explain why earlier studies that considered asbestos mostly failed to find a significant dose-response relationship.
• Limitations the authors state:
  • DME exposure was self-reported, so differential misclassification bias cannot be completely excluded.
  • Retrospective exposure assessment in case-control studies is open to debate.
  • Residual confounding by smoking has to be considered as an explanation of the results.
  • Among men never exposed to asbestos there were almost no men with high diesel exposure.
  • Women were excluded because very few reported DME exposure.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Lung Cancer, Dose-response relationship, Asbestos Exposure, Case-Control Study, Cumulative Exposure.

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