The epidemiologic evidence for elongate mineral particle (EMP)-related human cancer risk

Our plain-English summary of The epidemiologic evidence for elongate mineral particle (EMP)-related human cancer risk, by P. Boffetta, K.A. Mundt, W.J. Thompson (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: P. Boffetta, K.A. Mundt, W.J. Thompson
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:100-106
• Type of article: Review
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Epidemiologic research on the role of fibers and other elongate mineral particles (EMP) and human diseases including cancers has generated a large body of literature over the last decades: nevertheless, there remain some questions for which the scientific community appears unable to reach consensus. Reasons for genuine differences in opinion include (i) ways in which exposures have been classified; (ii) methodological limitations of the available studies, (iii) criteria for the interpretation of study results, including potential underlying biological mechanisms, and (iv) methodology for integrating the evidence. Various approaches have been proposed in recent years to address these issues, which will be illustrated using examples from asbestos, talc, taconite, synthetic mineral fibers and silicon carbide, with emphasis on potential carcinogenic effects. Potential solutions include improved exposure and outcome assessment - including use of biomarkers and other molecular approaches, consideration of potential confounding and other sources of bias, implementation of guidelines for study quality assessment and evidence evaluation and integration.

Copyright © 2018. Published by Elsevier Inc.

In plain English

This article was a review, not a new study. The authors did not review all studies. They used selected examples to discuss methods problems in research on elongate mineral particles (EMPs), which they defined as mineral particles of inhalable, thoracic or respirable size that are at least three times longer than wide. Drawing on an earlier systematic review of 56 asbestos-exposed worker cohorts, they reported that the share of deaths from pleural cancer differed by fiber type (p-value 0.00003), and most cohorts with a share below 1% were chrysotile-exposed. They called this indirect evidence of a lower mesothelioma risk from chrysotile than from amphiboles. Their pooled analysis of five cohorts exposed to talc with no or minimal asbestos contamination gave a lung cancer estimate of 1.15 (95% CI 0.95-1.38, 131 deaths). They also discussed published studies of taconite iron ore miners, synthetic vitreous fiber workers and Norwegian silicon carbide workers. They argued that asbestos exposure in other jobs, smoking and poor exposure measurement complicate how those studies can be read. The authors concluded that the evidence does not give enough clarity to confidently conclude that EMPs other than very long, thin single-crystal structures are associated with pleural or lung cancers.

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 selected published epidemiologic studies, not a systematic review. It includes the authors' own pooled (meta-)analysis of talc cohorts and draws on an earlier systematic review of asbestos cohorts.
• Who was studied: Published studies of exposed groups, mainly worker cohorts: asbestos-exposed cohorts, talc miners and millers, Minnesota taconite and hematite iron ore miners, synthetic vitreous fiber production workers, and silicon carbide workers in Norway and Montreal
• Exposure: Elongate mineral particles, defined as mineral particles of inhalable, thoracic or respirable size with a length-to-width ratio of at least 3:1. Examples were commercial asbestos (chrysotile, amphiboles including crocidolite and amosite), talc, taconite, synthetic vitreous fibers (rock wool, glass wool, continuous glass filament) and silicon carbide. Studies of erionite, fluoro-edenite, nephrite and Libby amphiboles were excluded.
• Main results:
  • In 56 asbestos-exposed occupational cohorts (22 chrysotile, 8 amphiboles, 26 mixed or unknown), fiber type was strongly correlated with the proportion of pleural cancer deaths among all deaths (p-value of difference 0.00003)
  • The authors described this as indirect evidence of a lower mesothelioma risk from chrysotile than from amphibole or mixed commercial asbestos
  • The authors' random-effect meta-analysis of five cohorts of miners and millers of talc not contaminated with asbestos gave a pooled lung cancer SMR of 1.15 (95% CI 0.95-1.38, 131 deaths). Table 1 lists no mesothelioma deaths in these cohorts.
  • In a cited case-control study of Minnesota iron ore miners (Lambert et al., 2016), mesothelioma risk was lowest in the eastern zone (Zone 4 taconite years RR=0.97, 95% CI 0.92-1.03), where taconite EMPs were most common
  • In a cited nested case-control study of taconite workers (Allen et al., 2015b), lung cancer was not related to taconite years (RR=0.99, 95% CI 0.96-1.01) after adjustment for hematite, silica and asbestos exposure and sex
  • In the cited US rock wool production worker cohort (Marsh et al., 2001), 1 pleural cancer death was observed against 2.53 expected (SMR 0.39; 95% CI 0.01 to 2.20). The authors judged that there is no consistent evidence of increased mesothelioma risk in synthetic vitreous fiber production workers.
  • In the cited study of 2613 male Norwegian silicon carbide production workers (Bugge et al., 2012), after adjustment for cristobalite or fibers there was no excess lung cancer risk from silicon carbide particles (RR 0.9; 95% CI 0.5-1.6)
• The authors' conclusion: The authors concluded that the evidence, though extensive, does not give sufficient clarity to confidently conclude that EMPs other than very long, thin monocrystalline structures are associated with pleural or lung cancers. They called for higher methodological standards and better characterization of particle shape.
• Limitations the authors state:
  • The ratio of mesothelioma or pleural cancer deaths to total deaths in the asbestos cohorts could not be adjusted for age at death, because this information was not in the published reports
  • Many of the available studies are affected by residual confounding, incomplete follow-up and poor exposure assessment

Topics

Medical terms in this study, explained in our Lexicon: elongate mineral particles (EMPs), Talc, Taconite, Mineral Fiber, Carcinogenic, Biomarker, Confounding.

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• Non-asbestiform elongate mineral particles and mesothelioma risk: Human and experimental evidence — J.E. Goodman, M.J. Becich, et al. (2023)
• Does qualitative examination of Elongated Mineral Particles (EMP) recovered from human and animal lungs provide reliable information on their carcinogenic and other effects? — B.W. Case (2018)
• Dosimetry of inhaled elongate mineral particles in the respiratory tract: The impact of shape factor — B. Asgharian, T.P. Owen, et al. (2018)
• Measurement of elongate mineral particles: What we should measure and how do we do it? — E.J. Chatfield (2018)

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