Relationship between exposure to ionizing radiation and mesothelioma risk: A systematic review of the scientific literature and meta-analysis

Our plain-English summary of Relationship between exposure to ionizing radiation and mesothelioma risk: A systematic review of the scientific literature and meta-analysis, by G. Visci, E. Rizzello, C. Zunarelli, et al (Cancer Medicine, 2022).

The study

• Authors: G. Visci, E. Rizzello, C. Zunarelli, F.S. Violante, P. Boffetta
• Journal: Cancer Medicine
• Published: 2022;11(3):778-789
• Type of article: Meta-analysis, Systematic review
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Ionizing radiation and mesothelioma have been examined among personnel employed in nuclear power plant and patients treated by external beam radiation therapy (EBRT). The association is still controversial; the purpose of this review is to summarize the scientific evidence published in the literature regarding the relationship between ionizing radiation and incidence of mesothelioma and, if possible, estimating strongness of the association by meta-analysis of extracted data.

Methods: Articles included in the systematic review were retrieved by searching among the three main scientific databases: PubMed, Scopus, and Embase. The literature search was conducted in June 2021. A meta-analysis of random effects was conducted, stratified by exposure (EBRT, occupational exposure). The heterogeneity of the summary relative risks (RRs) was assessed using I2 statistics. Publication bias was evaluated graphically through the funnel plot.

Findings: The exposure to ionizing radiation could be a risk factor for mesothelioma: both for exposure to high doses for short periods (EBRT) (RR of 3.34 [95% confidence interval, CI 1.24-8.99]) and for exposure to low doses for a prolonged duration (exposure working) (RR of 3.57 [95% CI 2.16-5.89]).

Conclusions: Despite the low number of mesotheliomas in the general population, the steadily increased risk among individuals exposed to radiation is still worth considering.

© 2022 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.

In plain English

This article was a systematic review and meta-analysis. The authors searched PubMed, Scopus and Embase in June 2021 for cohort or case-control studies of ionizing radiation and mesothelioma. They pooled nine cohort studies. Four were of patients given radiotherapy (external beam radiation therapy) after an earlier cancer, and five were of nuclear industry workers. No studies of Thorotrast patients were retained. For radiotherapy patients, the pooled relative risk of mesothelioma was 3.34 (95% CI 1.24 to 8.99). After one outlying study was removed, it was 1.72 (95% CI 1.24 to 2.38). For nuclear workers, the pooled relative risk was 3.57 (95% CI 2.16 to 5.89). The authors found no evidence of publication bias. None of the studies precisely estimated asbestos exposure, so results could not be corrected for it. The authors also could not study dose-response or separate pleural from peritoneal mesothelioma, and they noted possible misclassification of mesothelioma and low statistical power. The authors concluded that the evidence supported a causal connection between ionizing radiation and mesothelioma risk, but that they could not understand the role of asbestos and other confounders.

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 random-effects meta-analysis of published cohort studies, stratified by type of exposure (radiotherapy versus occupational)
• Who was studied: Nine cohort studies were pooled, out of 23 included in the review. Four studied radiotherapy patients (two in the USA, one in the Netherlands, one in Canada). Five studied nuclear industry workers (France, two in the USA, Australia, United Kingdom). The literature search was done in June 2021.
• Exposure: Ionizing radiation from external beam radiotherapy (high doses over short periods) and from occupational exposure in the nuclear industry (low doses over long periods), including uranium, gamma rays, neutrons, tritium, plutonium and other radionuclides. Thorotrast studies were not included. Asbestos exposure was not measured in the pooled studies.
• Main results:
  • Radiotherapy (EBRT) patients: summary relative risk of mesothelioma 3.34 (95% CI 1.24 to 8.99)
  • Radiotherapy patients, after excluding the outlying De Bruin et al. study: heterogeneity fell from 96.4% to 64.1%, and the summary relative risk was 1.72 (95% CI 1.24 to 2.38)
  • Nuclear industry workers: summary relative risk of mesothelioma 3.57 (95% CI 2.16 to 5.89)
  • No evidence of publication bias was found for either the radiotherapy studies or the nuclear worker studies
  • The authors stated that there did not appear to be a dose-response gradient in their results
• The authors' conclusion: The authors concluded that the evidence supported a causal connection between ionizing radiation exposure and mesothelioma risk. They added that they were unable to understand the role of other confounding factors such as asbestos and other carcinogens.
• Limitations the authors state:
  • No study gave a precise estimate of asbestos exposure, so the results could not be corrected for it
  • Mesothelioma may have been misclassified in the original studies, which may have led to underestimation of case numbers
  • Too little information on radiation dose to study the dose-response relationship
  • Pleural and peritoneal mesothelioma could not be evaluated separately
  • Small numbers of mesothelioma cases gave low statistical power

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Systematic Review, Meta-Analysis, Occupational Exposure, Relative Risk, confidence interval.

Related studies

• Re: Comment to "Relationship between exposure to ionizing radiation and mesothelioma risk: A systematic review of the scientific literature and meta-analysis": Cancer Med. 2022 Feb;11(3):778-789. doi: 10.1002/cam4.4436. Epub 2022 Jan 14: Cancer Med. 2022 Feb;11(3):778-789. doi: 10.1002/cam4.4436. Epub 2022 Jan 14 — G. Visci, C. Zunarelli, et al. (2022)
• Ionizing radiation: a risk factor for mesothelioma — J.E. Goodman, M.A. Nascarella, et al. (2009)
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• Risk of mesothelioma after cessation of asbestos exposure: a systematic review and meta-regression — P. Boffetta, F. Donato, et al. (2019)
• Occupational exposure to asbestos and risk of kidney cancer: an updated meta-analysis — C. Zunarelli, A. Godono, et al. (2021)

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