Cancer mortality in chrysotile miners and millers, Russian Federation: main results (Asbest Chrysotile Cohort-Study)

Our plain-English summary of Cancer mortality in chrysotile miners and millers, Russian Federation: main results (Asbest Chrysotile Cohort-Study), by J. Schüz, E. Kovalevskiy, A. Olsson, et al (Journal of the National Cancer Institute, 2024).

The study

• Authors: J. Schüz, E. Kovalevskiy, A. Olsson, M. Moissonnier, E. Ostroumova, G. Ferro, E. Feletto, S.J. Schonfeld, G. Byrnes, I. Tskhomariia, K. Straif, T. Morozova, H. Kromhout, I. Bukhtiyarov
• Journal: Journal of the National Cancer Institute
• Published: 2024;116(6):866-875
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: We investigated mortality in workers of the world's largest chrysotile mine and enrichment factories located in the town of Asbest, Russian Federation.

Methods: This historical cohort study included all workers employed for at least 1 year between 1975 and 2010 and follow-up until the end of 2015. Cumulative exposure to dust was estimated based on workers' complete occupational history linked to dust measurements systematically collected from the 1950s. Exposure to chrysotile fibers was estimated using dust-to-fiber conversion factors. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated as mortality rate ratios in Poisson regression models.

Results: A total of 30 445 (32% women) workers accumulated 721 312 person-years at risk and 11 110 (36%) died. Of the workers, 54% had more than 30 years since their first exposure. We found an exposure-response between cumulative dust and lung cancer mortality in men. No clear association with dust exposure but a modest increase in the highest category of fiber exposure was seen for lung cancer in women. Mesothelioma mortality was increased (RR = 7.64, 95% CI = 1.18 to 49.5, to at least 80 fibers per cm3 years and RR = 4.56, 95% CI = 0.94 to 22.1, to at least 150 mg/m3 years [dust]), based on 13 deaths. For colorectal and stomach cancer, there were inconsistent associations. No associations were seen for laryngeal or ovarian cancer.

Conclusion: In this large-scale epidemiological study in the world's largest active asbestos mine, we confirmed an increased risk of mesothelioma with high fiber exposure and an increasing mortality for lung cancer in men with increasing dust exposure. Less clear-cut increased lung cancer mortality was seen in the women. Continued mortality follow-up is warranted.

© The Author(s) 2024. Published by Oxford University Press.

In plain English

This historical cohort study followed 30 445 workers (32% women) employed at least 1 year between 1975 and 2010 at the chrysotile mine and enrichment factories in Asbest, Russian Federation. Follow-up ran to the end of 2015; 11 110 workers died. Cumulative dust exposure came from more than 90 000 workplace measurements; chrysotile fiber exposure was mainly modeled from dust. In men, lung cancer death rates rose with cumulative dust exposure: at 150 or more mg/m3-years the relative risk was 1.40 (95% CI 1.03 to 1.90), versus more than 0 to under 20. Women had 41 lung cancer deaths and no association with dust. There were 13 mesothelioma deaths, 2 of them in women. At 80 or more fibers/cm3-years the relative risk was 7.64 (95% CI 1.18 to 49.46), versus 0 to under 40 (the two lowest exposure thirds combined). Laryngeal and ovarian cancer showed no increases; stomach and colorectal results were inconsistent. The authors concluded that mesothelioma risk was increased with high chrysotile fiber exposure. The study lacked individual smoking and alcohol data and counted deaths, not diagnoses.

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: Historical (retrospective) cohort study using company records and death registers, analyzed with Poisson regression
• Who was studied: 30 445 workers (20 662 men, 9783 women) with at least 1 cumulative year of employment between 1975 and 2010 at the PJSC Uralasbest mine and enrichment factories in Asbest, Sverdlovsk Region, Russian Federation. Follow-up ran from 1976 to December 31, 2015, giving 721 312 person-years at risk; 11 110 workers died.
• Exposure: Cumulative exposure to airborne dust (mg/m3-years) was estimated for each worker's whole work history using a company-specific job-exposure matrix. Cumulative chrysotile fiber exposure (fibers/cm3-years) was mainly modeled from dust using dust-to-fiber conversion factors. A 5-year lag was applied.
• Main results:
  • Men, 564 lung cancer deaths: compared with more than 0 to 20 mg/m3-years of dust, relative risks were 1.20 (95% CI 0.92 to 1.57) at 20 to under 65, 1.37 (1.04 to 1.80) at 65 to under 150, and 1.40 (1.03 to 1.90) at 150 or more (P trend .02). Associations were somewhat weaker for fibers; the highest fiber category (80 or more) gave 1.26 (0.92 to 1.72).
  • Women, 41 lung cancer deaths: no association with cumulative dust (P trend 1.00). In the highest fiber category (80 or more fibers/cm3-years) the relative risk was 1.21 (95% CI 0.48 to 3.04).
  • Mesothelioma, men and women combined, 13 deaths (2 in women). The two lowest exposure tertiles had to be combined as the reference group because the lowest tertile had no mesothelioma deaths. For fibers, compared with 0 to under 40 fibers/cm3-years, relative risks were 6.27 (95% CI 1.10 to 35.84) at 40 to under 80 and 7.64 (1.18 to 49.46) at 80 or more. For dust, compared with 0 to under 65 mg/m3-years, relative risks were 2.54 (0.53 to 12.07) at 65 to under 150 and 4.56 (0.94 to 22.14) at 150 or more.
  • Laryngeal cancer (analyzed in men only, 46 deaths; women had only 1 case): no increase with increasing dust or fiber exposure.
  • Ovarian cancer (35 deaths in women): no association with dust or fiber exposure.
  • Stomach cancer: rate ratios were raised in men, but all confidence intervals included 1.00; in women all rate ratios were decreased.
  • Colorectal cancer: rate ratios were raised in all exposure categories in men (for example 1.96, 95% CI 1.01 to 3.82, at 80 or more fibers/cm3-years) but not in women. The authors called these findings difficult to interpret.
  • Overall mortality was lower in men with higher cumulative dust exposure, driven by inverse associations with alcohol-related noncancer diseases, infectious respiratory diseases and external causes. The authors attributed this to a healthy worker survivor effect.
  • Seven workers died of asbestosis.
• The authors' conclusion: The authors concluded that risk of mesothelioma was increased with high exposure to chrysotile fibers, with men more affected than women despite women's slightly higher cumulative exposure. They also concluded that lung cancer mortality in men increased with increasing cumulative dust exposure. In women they saw no increase with dust but a modest increase in the highest fiber category.
• Limitations the authors state:
  • There was no individual information on lifestyle factors such as smoking and alcohol consumption.
  • The study measured deaths, not new cases of disease.
  • Some exposure misclassification is present.
  • Workers who migrated from the region had to be censored at the date they were last known to be alive.
  • Differences between men and women could be due to chance, because there were few lung cancer deaths in women.
  • Some confounding by smoking in women cannot be ruled out.
  • Other lung carcinogens were present at the site, mainly for male workers: crystalline silica-containing dust, welding fumes and diesel engine exhaust. These were not quantified.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Cohort Study, Cumulative Exposure, Occupational History, Relative Risk, confidence interval, rate ratio, Lung Cancer.

Related studies

• Occupational cohort study of current and former workers exposed to chrysotile in mine and processing facilities in Asbest, the Russian Federation: Cohort profile of the Asbest Chrysotile Cohort study — J. Schüz, I. Bukhtiyarov, et al. (2020)
• Tobacco smoking among chrysotile asbestos workers in Asbest in the Russian Federation — A. Olsson, E.V. Kovalevskiy, et al. (2020)
• Comparison of Two Information Sources for Cause-of-Death Follow-up in the Russian Federation: The Asbest Chrysotile Cohort Study — J. Schüz, E. Kovalevskiy, et al. (2020)
• A comparison of parallel dust and fibre measurements of airborne chrysotile asbestos in a large mine and processing factories in the Russian Federation — E. Feletto, S.J. Schonfeld, et al. (2017)
• A retrospective cohort study of cancer mortality in employees of a Russian chrysotile asbestos mine and mills: study rationale and key features — J. Schüz, S.J. Schonfeld, et al. (2013)
• Developing a company-specific job exposure matrix for the Asbest Chrysotile Cohort Study — E. Feletto, E.V. Kovalevskiy, et al. (2022)

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