Asbestos-related lung cancer and malignant mesothelioma of the pleura: selected current issues

Our plain-English summary of Asbestos-related lung cancer and malignant mesothelioma of the pleura: selected current issues, by S. Markowitz (Seminars in Respiratory and Critical Care Medicine, 2015).

The study

• Author: S. Markowitz
• Journal: Seminars in Respiratory and Critical Care Medicine
• Published: 2015;36(3):334-46
• Type of article: Review
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos-related diseases persist, because millions of workers have had prior exposure and many industrializing countries continue to use asbestos. Globally, an estimated 107,000 people die annually from lung cancer, malignant mesothelioma, and asbestosis due to occupational asbestos exposure. Malignant mesothelioma and lung cancer are caused by all major types of asbestos. Asbestos causes more lung cancer deaths than malignant mesothelioma of the pleura; most cases of the latter are due to asbestos exposure. The cancer risk increases with cumulative asbestos exposure, with increased risk even at low levels of exposure to asbestos. Based on empirical studies, an estimated cumulative occupational exposure to asbestos of 1 fiber/mL-year substantially raises malignant mesothelioma risk. No safe threshold for asbestos exposure has been established for lung cancer and mesothelioma. The validity of fiber-type risk assessments depends critically on the quality of exposure assessments, which vary considerably, leading to a high degree of uncertainty. Asbestos exposure without asbestosis and smoking increases the risk of lung cancer. The joint effect of asbestos and smoking is supra-additive, which may depend in part on the presence of asbestosis. Asbestos workers who cease smoking experience a dramatic drop in lung cancer risk, which approaches that of nonsmokers after 30 years. Studies to date show that longer, thinner fibers have a stronger association with lung cancer than shorter, less thin fibers, but the latter nonetheless also show an association with lung cancer and mesothelioma. Low-dose chest computed tomographic scanning offers an unprecedented opportunity to detect early-stage lung cancers in asbestos-exposed workers.

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In plain English

This article is a single-author review, with no new data, of selected issues in asbestos-related lung cancer and pleural malignant mesothelioma. The author summarized published studies and stated that all major asbestos types, including chrysotile, cause both diseases. In case–control studies from France, Germany and Spain, mesothelioma risk rose with occupational asbestos exposure. In one French study, cumulative exposure of 0.5 to 0.99 fiber/mL-year was associated with an odds ratio of 4.2 (95% CI 2.0 to 8.8). A cited study compared North American insulators with unexposed blue-collar controls. Smoking controls had a lung cancer mortality rate ratio of 10.3 (95% CI 8.8 to 12.2), so the baseline was non-smoking controls. Never-smoking insulators without asbestosis had 3.6 (95% CI 1.7 to 7.6), and smoking insulators with asbestosis had 36.8 (95% CI 30.1 to 45.0). The author noted that many exposure assessments were lacking, which makes comparisons of potency between fiber types uncertain. The author concluded that no safe exposure threshold has been shown and that low-dose CT scanning offers an opportunity to detect early lung cancers in asbestos-exposed workers.

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: Narrative review of published epidemiological, animal, fiber burden, mechanistic and screening studies (no new data collected)
• Who was studied: No study population of its own. The review draws on published cohort and case–control studies of asbestos-exposed workers and community residents in many countries, including case–control studies of mesothelioma from France, Germany and Spain summarized in Table 1.
• Exposure: Occupational and non-occupational asbestos exposure of all major types (chrysotile, crocidolite, amosite, anthophyllite, tremolite, actinolite), and cigarette smoking as a joint factor for lung cancer
• Main results:
  • In a cited French case–control study (Iwatsubo and colleagues), cumulative asbestos exposure of 0.5 to 0.99 fiber/mL-year was associated with a mesothelioma odds ratio of 4.2 (95% CI 2.0 to 8.8). Higher doses led to higher risks.
  • In a cited second French case–control study of pleural mesothelioma (Lacourt and colleagues), men with cumulative exposure below 0.1 fiber/mL-year had an odds ratio of 4.0 (99% CI 1.9 to 8.3).
  • In a cited study of 2,377 North American insulators (Markowitz and colleagues), the smoking control group without asbestos exposure had a lung cancer mortality rate ratio of 10.3 (95% CI 8.8 to 12.2), on the same scale as the insulator figures.
  • In the same insulator study, never-smoking insulators without asbestosis had a lung cancer mortality rate ratio of 3.6 (95% CI 1.7 to 7.6), compared with the blue-collar controls.
  • In the same insulator study, insulators who had smoked and also had asbestosis had a lung cancer mortality rate ratio of 36.8 (95% CI 30.1 to 45.0).
  • In the same insulator study, former smoking insulators who had quit about 30 or more years earlier had the same lung cancer risk as insulators who had never smoked. The comparison symbol before '30' is lost in the text.
  • In a cited follow-up of a South Carolina textile factory where more than 99.9% of the asbestos used was chrysotile (Hein and colleagues), the lung cancer standardized mortality ratio was 1.95 (95% CI 1.68 to 2.24).
  • After a new North Carolina textile study, Hodgson and Darnton revised their mesothelioma potency ratios downwards sevenfold, to 70:14:1 for crocidolite to amosite to chrysotile.
  • In the Carolina textile studies, the strongest lung cancer association was with fibers longer than 10 µm and narrower than 0.25 µm, but very short and thin fibers were also associated with lung cancer risk.
  • In the cited National Lung Screening Trial, the CT-screened arm had a significant 20% reduction in lung cancer mortality compared with chest radiograph. Occupational risk of lung cancer was not a risk factor included in the studies.
• The authors' conclusion: The author concluded that there is no known safe level of asbestos exposure for lung cancer and mesothelioma, and that low-dose chest CT scanning offers an opportunity to detect early-stage lung cancers in asbestos-exposed workers.
• Limitations the authors state:
  • The author states that exposure assessments in many of the studies used to estimate fiber-type potency were lacking, for numerous reasons.
  • The author cites the International Agency for Research on Cancer's conclusion that relative potency estimates carry a high degree of uncertainty.
  • The author states that studying the joint effect of asbestos and smoking is hampered by the small number of lung cancers among never smokers.
  • The author states that fiber size categories were highly correlated in the Carolina textile dust samples, making it difficult to separate the effects of fiber sizes.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, Pleura, Asbestos Exposure, Occupational Exposure, No Safe Level of Exposure.

Related studies

• Asbestos-related diseases in Italy: epidemiologic evidences and public health issues — P. Comba, E. Merler, et al. (2005)
• Current issues in the pathologic and mineralogic diagnosis of asbestos-induced disease — A. Churg (1983)
• Current issues in malignant pleural mesothelioma evaluation and management — J. Ai, J.P. Stevenson (2014)
• Current issues regarding the pathobiology of asbestosis: a chronologic perspective — E. Kagan (1988)
• Low-dose CT: a useful and accessible tool for the early diagnosis of lung cancer in selected populations — L. Callol, F. Roig, et al. (2007)
• Current approach to malignant mesothelioma of the pleura — J. Aisner (1995)

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