Occupational Asbestos Exposure and Kidney Cancer: Systematic Review and Meta-analysis of Cohort Studies

Our plain-English summary of Occupational Asbestos Exposure and Kidney Cancer: Systematic Review and Meta-analysis of Cohort Studies, by C.C.Y. Pang, K. Phan, M.N. Karim, et al (Annals of Work Exposures and Health, 2021).

The study

• Authors: C.C.Y. Pang, K. Phan, M.N. Karim, A. Afroz, M. Winter, D.C. Glass
• Journal: Annals of Work Exposures and Health
• Published: 2021;65(3):255-265
• Type of article: Meta-analysis, Systematic review
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: An estimated 125 million workers are exposed to asbestos worldwide. Asbestos is classified by the International Agency for Research on Cancer as a Group 1 carcinogen. The association between occupational asbestos exposure and kidney cancer is not well established however. This study aimed to determine the mortality and incidence of kidney cancer in workers who have been exposed to asbestos. We performed a systematic review and meta-analysis to evaluate the association between occupational asbestos exposure and kidney cancer.

Methods: Medline, EMBASE, and Web of Science were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for articles on occupational asbestos exposure and kidney cancer. The studies reported the standardized mortality ratio (SMR) or standardized incidence ratio (SIR) of kidney cancer in workers exposed to asbestos. SMRs or SIRs with its 95% confidence interval (CI) were pooled using a fixed-effect model.

Results: Forty-nine cohort studies involving 335 492 workers were selected for analysis. These studies included 468 kidney cancer deaths and 160 incident cases. The overall pooled-SMR of kidney cancer was 0.95 (95% CI: 0.86-1.05), with no significant heterogeneity (PQ = 0.09, I2 = 24.87%). The overall pooled-SIR of kidney cancer was 0.95 (95% CI: 0.79-1.11), with no significant heterogeneity (PQ = 0.68, I2 = 0.00%). Subgroup analysis did not find any increased association with occupational asbestos exposure. There was no evidence of publication bias with Egger's test P values of 0.08 for mortality studies and 0.99 for incidence studies.

Conclusions: This systematic review and meta-analysis did not show evidence of association between occupational asbestos exposure and kidney cancer mortality or incidence.

© The Author(s) 2020. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

In plain English

This was a systematic review and meta-analysis, which pooled results from earlier studies rather than following workers directly. The authors searched Medline, EMBASE and Web of Science up to 31 December 2019 for cohort studies of workers occupationally exposed to asbestos that reported kidney cancer deaths or new cases. They included 49 cohort studies from 45 articles: 276 214 workers in mortality studies and 59 278 in incidence studies, with 468 kidney cancer deaths and 160 new kidney cancer cases. Each study compared the workers with the general population. Overall, kidney cancer deaths among exposed workers were 0.95 times the number expected (95% CI 0.86 to 1.05), and new cases were 0.95 times expected (95% CI 0.79 to 1.11). Neither figure was statistically significant. Separate results for chrysotile and amphibole exposure, for different industries, and for the four mortality studies with adequate exposure assessment did not show raised kidney cancer. The authors concluded that the analysis showed a lack of association between occupational asbestos exposure and kidney cancer risk. They noted several weaknesses that could have pushed results toward finding no effect. These included missing dose data, possibly too-short follow-up, and earlier deaths from other asbestos diseases.

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: Systematic review and meta-analysis of cohort studies (pooled standardized mortality ratios and standardized incidence ratios)
• Who was studied: 49 cohort studies from 45 articles, published 1979 to 2018 and found by searches up to 31 December 2019. They covered 276 214 workers in mortality studies and 59 278 workers in incidence studies in Europe, North America, Asia and Australia. Ninety-two percent were male.
• Exposure: Occupational asbestos exposure, mainly in mining, textile, cement and insulation work. Other workers were in shipyards, ship breaking, the rail industry, asbestos plants and friction material manufacturing. Fiber types were grouped as chrysotile, amphibole or undefined.
• Main results:
  • The included studies contained 468 kidney cancer deaths across 38 mortality studies and 160 incident kidney cancer cases across 11 incidence studies.
  • Across the mortality studies, the pooled standardized mortality ratio (fixed-effects) for kidney cancer was 0.95 (95% CI 0.86 to 1.05), which was not statistically significant.
  • Across the incidence studies, the pooled standardized incidence ratio (fixed-effects) for kidney cancer was 0.95 (95% CI 0.79 to 1.11).
  • Among the mortality studies, the pooled ratio was 0.73 (95% CI 0.46 to 1.01) for chrysotile exposure and 0.65 (95% CI 0.25 to 1.06) for amphibole exposure.
  • Among the incidence studies, the pooled ratio was 0.93 (95% CI 0.47 to 1.4) for chrysotile exposure and 0.83 (95% CI 0.57 to 1.09) for amphibole exposure.
  • Textile workers in four mortality studies had a pooled ratio of 0.47 (95% CI 0.04 to 0.91), meaning fewer kidney cancer deaths than expected. The authors described this as marginally statistically significant.
  • The four mortality studies with adequate exposure assessment had a pooled ratio of 0.65 (95% CI 0.30 to 1.00).
  • Leaving out the Harding study changed the pooled mortality ratio to 0.88 (95% CI 0.78 to 0.98). The authors reported the Harding study as the only included mortality study with a statistically significant positive association.
  • Egger's test did not show evidence of publication bias: p = 0.08 for mortality studies and p = 0.99 for incidence studies.
• The authors' conclusion: The authors concluded that the meta-analysis showed a lack of association between occupational asbestos exposure and kidney cancer risk, with no clear dose-response relationship. They stated that weaknesses in the individual studies prevented establishing asbestos as a potential cause of kidney cancer.
• Limitations the authors state:
  • There was not enough exposure data to examine a dose-response relationship.
  • The latent period may have been too short for kidney cancers to develop.
  • Because kidney cancer has high survival and workers may have died of other causes such as lung cancer, kidney cancer deaths may have been under-reported.
  • The general-population comparison groups may have included asbestos-exposed people, potentially biasing results toward the null.
  • Some studies relied on self-reported questionnaires for occupational history.
  • There was no information on workers' later jobs, where they may have been exposed to other chemical hazards.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Systematic Review, Meta-Analysis, standardized mortality ratio (SMR), Standardized Incidence Ratio (SIR), confidence interval.

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• Asbestos and kidney cancer: the evidence supports a causal association — A.H. Smith, V.I. Shearn, et al. (1989)
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