Association between mesothelioma and non-occupational asbestos exposure: systematic review and meta-analysis

Our plain-English summary of Association between mesothelioma and non-occupational asbestos exposure: systematic review and meta-analysis, by R. Xu, F.K. Barg, E.A. Emmett, et al (Environmental Health, 2018).

The study

• Authors: R. Xu, F.K. Barg, E.A. Emmett, D.J. Wiebe, W.T. Hwang
• Journal: Environmental Health
• Published: 2018;17(1):90
• Type of article: Meta-analysis, Systematic review
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The risk of mesothelioma has been shown to be associated with exposure to asbestos fibers. Most of the existing literature focuses on occupational exposure; however, non-occupational asbestos exposure has also been identified as an important risk factor.

Objective: To estimate the association between mesothelioma and non-occupational asbestos exposure, and evaluate control recruitment and exposure measurement methods.

Methods: A systematic literature review was conducted to identify case-control (CC) and cohort studies that examined the association between mesothelioma and non-occupational exposure to asbestos, including neighborhood, domestic, and household exposure. Meta-analysis was performed to estimate a summary relative risk estimate (SRRE) and 95% confidence interval using random-effects models. Subgroup analyses were also conducted by exposure type, gender, region, and fiber type.

Results: Twenty CC and 7 cohort studies were selected. Controls in CC studies were selected from the general population (55%), hospital records (18%), cancer registry (23%) and a combination of population and hospital records (5%). Multiple methods were used to measure neighborhood exposure (e.g., linear distance and direction of residence from an asbestos factory), domestic (e.g., whether living with an asbestos worker) and household exposure (e.g., whether involved in asbestos-containing home improvement projects). Primary meta-analyses suggested a SRRE of mesothelioma of 5.33 (95%CI: 2.53, 11.23) from neighborhood exposure, 4.31 (95%CI, 2.58, 7.20) from domestic exposure, and 2.41 (95%CI, 1.30, 4.48) from household exposure with large I2 statistics ranging from 83-99%.

Conclusions: Non-occupational asbestos exposure is significantly associated with an elevated risk of mesothelioma. Funnel plots indicated a potential of publication bias. Some SRREs should be interpreted with cautions because of high between-studies heterogeneity.

In plain English

This was a systematic review and meta-analysis. The authors searched PubMed, with no date limit, for case-control and cohort studies of mesothelioma and non-occupational asbestos exposure. They found 27 eligible studies (20 case-control, 7 cohort) and pooled 24. Exposure was grouped as neighborhood (living near asbestos sites), domestic (fibers brought home by, or living with, asbestos workers) or household (asbestos-containing home materials, hobbies or home improvement projects). Including studies with mixed exposures, pooled relative risks were 5.33 (95% CI 2.53 to 11.23) for any neighborhood, 4.31 (2.58 to 7.20) for any domestic and 2.41 (1.30 to 4.48) for any household exposure. For household exposure alone (four studies), the estimate was 1.73 (95% CI 0.93 to 3.23), not statistically significant. Pooled estimates were higher for women than men, and higher in cohort than case-control studies. The three chrysotile-specific studies gave a non-significant estimate. Funnel plots suggested possible publication bias. The authors concluded that non-occupational exposure was associated with elevated mesothelioma risk. They urged caution because of high between-study variation, few studies, unclear exposure definitions and missing information on pleural versus peritoneal mesothelioma.

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 case-control and cohort studies, pooled with random-effects models
• Who was studied: Published case-control and cohort studies found through PubMed (no date restriction) and reference lists: 27 eligible studies (20 case-control, 7 cohort), 24 of them included in the meta-analysis. The studies came from Europe, the USA/Canada, Turkey, Egypt, South Africa, Australia and New Caledonia.
• Exposure: Non-occupational asbestos exposure, grouped into three types. Neighborhood exposure meant living near asbestos factories or naturally occurring asbestos. Domestic exposure meant fibers brought home by asbestos workers, or living with occupationally exposed people. Household exposure meant asbestos-containing materials in home structures, home-based hobbies or home improvement projects. Fiber types, where reported, included chrysotile, crocidolite, tremolite, amosite and mixed fibers.
• Main results:
  • Any neighborhood exposure (16 studies: 14 neighborhood-only plus 2 with mixed exposures): pooled relative risk 5.33 (95% CI 2.53, 11.23), with I2 of 99% (very high variation between studies)
  • Neighborhood-only exposure (14 studies): pooled relative risk 5.88 (95% CI 2.62, 13.16)
  • Any neighborhood exposure, after removing the Turkish study that reported a relative risk of 77.17: pooled relative risk 4.31 (95% CI 2.16, 8.61)
  • Any domestic exposure: pooled relative risk 4.31 (95% CI 2.58, 7.20), after three studies with mixed exposure were added to the domestic-only studies. The 12 domestic-only studies gave 4.64 (95% CI 2.49, 6.63), with I2 of 86.3%.
  • Household exposure only (4 studies): non-significant pooled relative risk 1.73 (95% CI 0.93, 3.23)
  • Any household exposure (6 studies, including mixed exposures): pooled relative risk 2.41 (95% CI 1.30, 4.48), with I2 of 87.3%
  • Any non-occupational exposure, by sex: pooled relative risk 4.80 (95% CI 1.96, 11.76) for males (7 studies) and 7.83 (95% CI 3.30, 18.57) for females (10 studies)
  • The three studies reporting chrysotile-specific risk gave a pooled relative risk of 3.56 (95% CI 0.65, 20.82) for any non-occupational exposure, which was not statistically significant
  • Pooled estimates from cohort studies (8.17 to 12.62 depending on exposure type) were higher than those from case-control studies (about 2 to 4)
  • The 7 highest-quality (Tier 1) studies combined gave a pooled relative risk of 3.56 (95% CI 1.61, 7.89), with I2 of 94.2%
  • Funnel plots for all three exposure types suggested possible publication bias
• The authors' conclusion: The authors concluded that there was a positive and strong association between non-occupational asbestos exposure and mesothelioma risk, with elevated risk for all three exposure types. Because of large heterogeneity and possible publication bias, they said caution is needed in interpreting the findings, and they called for clearer exposure definitions and rigorously conducted studies.
• Limitations the authors state:
  • Few studies were available for the meta-analysis
  • Some studies had small sample sizes, making their individual estimates very uncertain
  • Heterogeneity between studies was large (I2 above 80% for all exposure types), possibly because definitions of non-occupational exposure were unclear and overlapping
  • Many studies did not report key characteristics, such as pleural versus peritoneal mesothelioma, so no analysis by mesothelioma type was possible
  • The results may be affected by publication bias. The authors also suggested that the lack of studies showing negative associations could instead reflect a strong true association.
  • The fiber-type subgroup results are based on few studies, and fiber type may have been misclassified (for example, erionite misclassified as tremolite in earlier studies)

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, Asbestos Exposure, Systematic Review, Meta-Analysis, Occupational Exposure, Non-Occupational Exposure, Relative Risk, confidence interval.

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