An overview of the risk of lung cancer in relation to exposure to asbestos and of taconite miners

Our plain-English summary of An overview of the risk of lung cancer in relation to exposure to asbestos and of taconite miners, by G. Berry, G.W. Gibbs (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: G. Berry, G.W. Gibbs
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S218-22
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Exposure-response relationships between the relative risk of lung cancer and quantitative measures of exposure to asbestos are available from a number of epidemiological studies. Meta-analyses of these relationships have been published by Lash et al. (1997) [Lash, T.L., Crouch, E.A.C., Green, L.C., 1997. A meta-analysis of the relation between cumulative exposure to asbestos and relative risk of lung cancer. Occup. Environ. Med. 54, 254-263] and Hodgson and Darnton (2000) [Hodgson, J.T., Darnton, A., 2000. The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure. Ann. Occup. Hyg. 44, 565-601]. In this paper, the risks derived in these meta-analyses have been compared. Lash et al., concentrated on process and found that the risk of lung cancer increased as the asbestos is refined by processing. Hodgson and Darnton concentrated on fibre type and found that the risk was highest for exposure to amphibole asbestos (crocidolite and amosite), lowest for chrysotile and intermediate for mixed exposure. Some of the differences between the conclusions from the two meta-analyses are a consequence of the choice of studies included. The range of asbestos types included in the studies in the analysis of Hodgson and Darnton was wider than that in Lash et al., enabling differences between fibre types to be analyzed more readily. There are situations where occupational exposure to chrysotile asbestos has shown no detectable increase in risk of lung cancer. Taconite miners have shown no increased risk of mortality due to lung cancer.

In plain English

This paper was a review. The authors compared two earlier meta-analyses of lung cancer risk and cumulative asbestos exposure: Lash et al. (1997, 15 cohorts) and Hodgson and Darnton (2000, 17 cohorts). Lash et al. found that risk rose with processing, from mining and milling to cement products to textiles and manufacturing. Hodgson and Darnton found the highest risk for crocidolite and amosite, much lower for chrysotile, and intermediate for mixed exposure. For the 11 shared studies, the excess risk per unit of exposure spanned over two orders of magnitude, excluding studies with a zero estimate in either analysis. Some disagreements, the authors said, reflected the choice of studies. They cited a friction products factory that processed chrysotile with no detectable increase in lung cancer. Reviewing two cohorts of taconite miners, they reported no excess of respiratory cancer deaths. They found no convincing evidence of increased lung cancer deaths among Homestake miners in South Dakota exposed to cummingtonite–grunerite. They noted uncertain historical exposure measurements. The authors concluded that asbestos exposure increases lung cancer incidence, that some occupational chrysotile exposures showed no detectable increase, and that taconite miners showed no increased lung cancer mortality.

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: Review (overview) comparing two published meta-analyses of exposure–response relationships for asbestos and lung cancer, plus a review of published cohort studies of taconite and cummingtonite–grunerite miners and one environmental exposure study
• Who was studied: The reviewed material included the meta-analyses of Lash et al. (15 cohorts) and Hodgson and Darnton (17 cohort studies), 11 of which were in both. It also included two taconite miner cohorts: 5751 Reserve Mining Company workers employed 1952–1976, and 3431 Minnesota men employed 1947–1958 at the Erie or Minntac operations. Three overlapping studies of Homestake miners in South Dakota were covered, as was a study of women living in two Quebec chrysotile mining areas, 1970–1989.
• Exposure: Cumulative asbestos exposure in fibres/ml years, by process (Lash et al.) and by fibre type: crocidolite, amosite, chrysotile, and mixed amphibole/chrysotile (Hodgson and Darnton). The review also covered taconite dust, cummingtonite–grunerite at the Homestake mine, and environmental (non-occupational) chrysotile exposure in Quebec.
• Main results:
  • In Lash et al., risk of lung cancer increased with processing. The increase in relative risk per fibre/ml year (k) was 0.00025 for mining and milling, 0.0034 for cement products and 0.0077 for manufacturing/textiles (0.0026 for all studies).
  • In Lash et al., adding a term for predominantly chrysotile use added no significant information. Its estimate was 0.19 (95% confidence interval 0.02–1.6).
  • In Hodgson and Darnton, the percentage excess risk per fibre/ml year (RL) was 4.2 for crocidolite, 5.2 for amosite, 0.47 for mixed amphibole/chrysotile and 0.062 for chrysotile.
  • For the 11 studies common to both meta-analyses, values of RL (the percentage excess risk per fibre/ml year) ranged over more than two orders of magnitude once studies with a zero value in either analysis were excluded. Six studies gave fairly similar values in the two analyses.
  • The authors attributed some differences between the meta-analyses' conclusions to the choice of studies. Hodgson and Darnton included a wider range of fibre types, including crocidolite and amosite mines.
  • At the Ferodo friction products factory in the north of England (Newhouse and Sullivan, 1989), chrysotile was processed with no detectable increase in lung cancer: 241 lung cancer deaths observed versus 242.5 expected (SMR 99). For men the figures were 229 versus 221.4 (SMR 103); for women, 12 versus 21.1 (SMR 57).
  • Among Reserve Mining Company taconite workers, there were 15 respiratory cancer deaths versus 18 expected (SMR 84). After 15 years latency there were 8 versus 7.9 expected (SMR 102), with no apparent exposure–response trends.
  • Among Erie and Minntac taconite miners and millers in Minnesota, there were 65 respiratory cancer deaths to 1988 versus 67 expected (SMR 97). There was no excess respiratory cancer mortality after a 10-year latency period.
  • For Homestake miners exposed to cummingtonite–grunerite, the authors found no convincing evidence of increased lung cancer deaths. One study's excess (10 respiratory cancer deaths versus 2.7 expected, SMR 370) was not supported by the two other studies (SMR 103 and SMR 102). In that study the relative risk was higher in the first 20 years after first exposure than later.
  • Among women in Quebec chrysotile mining areas (Camus et al.), there were 71 lung cancer deaths versus 71.4 expected. The authors judged an EPA model, which predicted 146 deaths, inappropriate. They found predictions from Hodgson and Darnton (76) and Lash et al. (73) in accord with the observed number when chance variation was considered.
• The authors' conclusion: The authors concluded that asbestos exposure increases lung cancer incidence, that there are situations where occupational chrysotile exposure has shown no detectable increase in risk, and that taconite miners have shown no increased risk of lung cancer mortality.
• Limitations the authors state:
  • Exposure measurements are uncertain because of changes in instruments, problems converting old measurements, lack of early systematic sampling and the use of guesses for early exposure. Relationships valid within a study may therefore be invalid outside it.
  • Hodgson and Darnton had to assume that the relative risk at zero exposure was 1, which is not necessarily true.
  • The Ontario study had only 21 lung cancer deaths, and no reliable exposure–response relationship could be fitted to it.
  • The studies in Lash et al. varied less in fibre type, leaving less opportunity to explore differences between fibre types.
  • Non-linearity or a threshold at low exposure is very difficult, perhaps impossible, to detect from epidemiological data. For a very low relative risk, whether any actual excess exists is not detectable.

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, Taconite, Relative Risk, Meta-Analysis, Cumulative Exposure, Mesothelioma, Asbestos Exposure, Amphibole Asbestos.

Related studies

• Risk assessment due to environmental exposures to fibrous particulates associated with taconite ore — R. Wilson, E.E. McConnell, et al. (2008)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)
• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• A case-control study of mesothelioma in Minnesota iron ore (taconite) miners — C.S. Lambert, B.H. Alexander, et al. (2016)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)
• Amphibole fibers in a taconite mine and in the lungs of the miners — B. Gylseth, T. Norseth, et al. (1981)

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