The interaction of asbestos and smoking in lung cancer: a modified measure of effect

Our plain-English summary of The interaction of asbestos and smoking in lung cancer: a modified measure of effect, by G. Berry, F.D. Liddell (The Annals of Occupational Hygiene, 2004).

The study

• Authors: G. Berry, F.D. Liddell
• Journal: The Annals of Occupational Hygiene
• Published: 2004;48(5):459-62
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The ratio of the relative risk of lung cancer due to asbestos exposure in non-smokers to that in smokers has been termed the relative asbestos effect (RAE). In a review, Liddell [Liddell FDK (2001) Ann Occup Hyg; 45: 341-56] estimated that the RAE was approximately 2. This measure is satisfactory when there is an appreciable relative risk due to asbestos but does not generalize to lower levels of exposure. A modified measure is proposed to overcome this difficulty. The modified measure, RAEm, is defined as the ratio of the excess relative risk (RR - 1) in non-smokers to that in smokers.

Methods: The cohort studies combined in Liddell's 2001 analysis have been used to give a combined estimate of the modified measure.

Results: The combined value of RAEm is 3.19 with 95% confidence interval 1.67-6.13.

Conclusion: The excess relative risk of lung cancer from asbestos exposure is about three times higher in non-smokers than in smokers. The modified measure has been placed within a more versatile model of interaction. If interaction is present the relative risk from asbestos exposure changes only slightly between light and heavy smokers, but is higher in very light smokers and non-smokers. The relative risk estimated from epidemiological studies of a mixed population of non-smokers and smokers applies to smokers.

In plain English

This paper proposed a modified measure of how asbestos exposure and cigarette smoking act together on lung cancer risk, applying it to seven cohort studies from an earlier review (Liddell, 2001). The earlier measure, the relative asbestos effect, was the ratio of the relative risk of lung cancer from asbestos in non-smokers to that in smokers. The authors argued it did not carry over to low exposures, so the new measure compared excess relative risks (the relative risk minus 1). Recalculated, the original measure was 2.05 (95% confidence interval 1.28–3.27). The combined modified measure was 3.19 (95% confidence interval 1.67–6.13), with no correction for differences between studies needed. The authors concluded that the excess relative risk of lung cancer from asbestos exposure is about three times higher in non-smokers than in smokers. From a hypothetical example, they judged that asbestos relative risks from mixed-population studies reasonably apply, within 10%, to light through very heavy smokers; only very light smokers and non-smokers would warrant higher values. They noted that dividing people only into smokers and non-smokers ignores how much they smoked.

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: Methodological paper proposing a new measure of interaction, illustrated by a meta-analysis (DerSimonian and Laird method) of cohort studies taken from an earlier review
• Who was studied: Results of seven cohort studies of asbestos-exposed workers that were included in the main analysis (Group A) of Liddell's 2001 review, with relative risks given separately for smokers and non-smokers
• Exposure: Asbestos exposure combined with cigarette smoking. Smoking was split into non-smokers and smokers. The paper's text does not specify fiber types.
• Main results:
  • Recalculated with the authors' variance method, the combined original measure (relative asbestos effect) across the seven studies was 2.05 (95% CI 1.28–3.27), close to the 2.04 (95% CI 1.28–3.25) in Liddell's 2001 review.
  • The combined modified measure (ratio of excess relative risk in non-smokers to that in smokers) across the seven studies was 3.19 (95% CI 1.67–6.13).
  • The heterogeneity test across studies gave Q = 5.59 with 6 degrees of freedom, so no correction for heterogeneity was needed.
  • For one study ([e]), a relative risk very close to 1 made the modified estimate highly unstable. That study carried only 0.1% of the weight in the modified-measure meta-analysis, compared with 25% in the original-measure meta-analysis.
  • The test that the modified measure exceeds 1 gave z = 3.50 on a log scale, compared with z = 3.14 for the original measure.
  • In a hypothetical worked example (modified measure of 3, and asbestos doubling risk in moderate smokers), the relative risk due to asbestos was 4.00 for non-smokers, 2.93 for very light smokers, 2.29 for light smokers, 2.00 for moderate smokers, 1.94 for heavy smokers and 1.90 for very heavy smokers.
  • In the same hypothetical example, a mixed population (40% non-smokers, 15% light, 30% moderate, 15% heavy smokers) gave an overall relative risk due to asbestos of 2.09, close to the moderate-smoker value.
• The authors' conclusion: The authors concluded that the excess relative risk of lung cancer from asbestos exposure is about three times higher in non-smokers than in smokers. They also judged that the relative risk due to asbestos estimated from studies of mixed populations can reasonably be taken, to within 10%, to apply to light, moderate, heavy and very heavy smokers. In their view a higher relative risk would be appropriate only for very light smokers and non-smokers.
• Limitations the authors state:
  • Both measures split smoking simply into non-smokers and smokers and make no allowance for the amount smoked.
  • Each modified-measure estimate is less precise than the original measure because its denominators are smaller, so its confidence intervals are wider.

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, Relative Risk, Asbestos Exposure, confidence interval.

Related studies

• Asbestos and lung cancer: an analysis of the epidemiological evidence on the asbestos-smoking interaction — R. Saracci (1977)
• Interaction of asbestos, age, and cigarette smoking in producing radiographic evidence of diffuse pulmonary fibrosis — K.H. Kilburn, R. Lilis, et al. (1986)
• Effects of asbestos and smoking on gas diffusion in people exposed to crocidolite — H.S. Alfonso, L. Fritschi, et al. (2005)
• The interactions of tobacco smoking and other agents in cancer etiology — R. Saracci (1987)
• Low-dose exposure to asbestos and lung cancer: dose-response relations and interaction with smoking in a population-based case-referent study in Stockholm, Sweden — P. Gustavsson, F. Nyberg, et al. (2002)
• Interaction between smoking and asbestos in human lung adenocarcinoma: role of K-ras mutations — H. Vainio, K. Husgafvel-Pursiainen, et al. (1993)

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