Clustering of malignant pleural mesothelioma in asbestos factories: a subgroup analysis in a 29-year follow-up study to identify high-risk industries in Taiwan

Our plain-English summary of Clustering of malignant pleural mesothelioma in asbestos factories: a subgroup analysis in a 29-year follow-up study to identify high-risk industries in Taiwan, by L.J. Lee, C.K. Lin, C.H. Pan, et al (BMJ Open, 2018).

The study

• Authors: L.J. Lee, C.K. Lin, C.H. Pan, Y. Cheng, Y.Y. Chang, S.H. Liou, J.D. Wang
• Journal: BMJ Open
• Published: 2018;8(12):e021063
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: Exposure to asbestos is the major cause for malignant pleural mesothelioma (MPM), but the causal link of individual cases is difficult to establish for lack of exposure information and long disease latency.

Methods: We established a retrospective cohort of workers employed in asbestos industries during the period of 1950-1989 and the occurrence of MPM during the period of 1980-2009 was examined with the Taiwan Cancer Registry. Estimated rate ratios (eRRs) were computed for each factory where any case of MPM was diagnosed by assuming Poisson distribution with a minimal latency of 20 years.

Results: A total of 18 MPM (17 males, 1 female) in eight factories were found. The incidence rate of MPM for the eight factories was 18.0 per million, ranging from 6.2 per million (military factory) to 268.2 per million (asbestos cement). We observed significantly increased risks for MPM in asbestos cement, thermal insulation and shipbuilding industries, with eRR (genders combined) of 113.6, 87.5 and 15.8, respectively. The sensitivity analyses considering latency showed similar findings in latency ≥30 years, and the shipbuilding industry presented a significant eRR given a latency ≥40 years. The gender-specific eRR showed similar results in men, but high eRR of 729.6 was observed in an asbestos cement factory where a female MPM was diagnosed.

Conclusions: This nationwide study in Taiwan comprehensively shows that different asbestos manufacturing processes, including asbestos cement, thermal insulation and shipbuilding industries, were at significantly increased risks for MPM. We recommend to establish a medical screening programme for workers previously exposed to asbestos to identify MPM and other asbestos-related diseases at an earlier stage.

© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This was a subgroup analysis within a retrospective cohort of workers from Taiwan's asbestos-related factories. Workers were identified from Labour Insurance records and linked to the Taiwan Cancer Registry for 1980 to 2009. The authors focused on 18 cases of malignant pleural mesothelioma (17 men, 1 woman) in eight factories. Each factory's rate was compared with Taiwan's general-population pleural cancer rate, used as a proxy, of 1.04 per million person-years, assuming at least 20 years' latency. The rate across the eight factories was 18.0 per million (95% CI 10.6 to 28.4). Estimated rate ratios, genders combined, were 113.6 (95% CI 12.8 to 410.0) for asbestos cement, 87.5 (9.8 to 315.9) for thermal insulation and 15.8 (7.9 to 28.2) for shipbuilding. The authors reported these as significantly increased. Single-case estimates for a sugar refinery, a military factory and a petrochemical factory had confidence intervals that included 1. The 18 cases had worked a mean of 7.7 years (range 0.1 to 30.0). The authors noted three limitations: they lacked long-term airborne fibre data, especially early on; age adjustment was impractical; and underdiagnosis may have caused risks to be underestimated.

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: Subgroup analysis of the mesothelioma cases within a retrospective cohort study, using record linkage between labour insurance and cancer registry data
• Who was studied: The full cohort was 183 560 workers ever employed in 389 asbestos-related factories in Taiwan, of whom 160 640 were followed from 1980 to 2009. The subgroup analysis covered the workers of the eight factories where mesothelioma cases occurred: 25 688 workers in the text, while Table 1 lists 31 210.
• Exposure: Employment in asbestos-related industries registered by Taiwan EPA. The eight factories with cases were in shipbuilding, asbestos cement, thermal insulation, a sugar refinery, a military factory and a petrochemical factory. No fiber types or measured fiber levels are given. All 18 cases began work before 1982, when the permissible exposure limit was 5 fibres/mL.
• Main results:
  • 18 malignant pleural mesothelioma cases (17 males, 1 female) were found, clustered in eight factories. No cases occurred in the other factories.
  • The incidence rate for the eight factories combined was 18.0 per million (95% CI 10.6 to 28.4). Individual factories ranged from 6.2 per million (military factory) to 268.2 per million (an asbestos cement factory). The comparison was the general population's rate of 1.04 per million person-years, which was the pleural cancer rate used as a proxy.
  • Estimated rate ratios (genders combined, latency of at least 20 years) were significantly increased in three industries: asbestos cement 113.6 (95% CI 12.8 to 410.0), thermal insulation 87.5 (9.8 to 315.9) and shipbuilding 15.8 (7.9 to 28.2).
  • In shipbuilding, nine cases occurred in a Northern shipbuilding factory, with an estimated rate ratio of 20.0 (95% CI 9.1 to 38.0). Two cases occurred in a Southern shipyard, with an estimated rate ratio of 8.0.
  • Three factories had one case each, and their estimated rate ratios had 95% confidence intervals that included 1: sugar refinery 8.8 (0.1 to 49.2), military factory 5.9 (0.1 to 33.1) and petrochemical 46.8 (0.6 to 260.1).
  • Among female workers, the one case in an asbestos cement factory gave an estimated rate ratio of 729.6 (95% CI 9.5 to 4059.3). Results for men alone were similar to those for genders combined.
  • In sensitivity analyses, results were similar with latency of at least 30 years. The shipbuilding industry had a significant estimated rate ratio with latency of at least 40 years.
  • The 18 cases first worked in the asbestos factories at a mean age of 28.1 years (range 15 to 48). Their mean work duration was 7.7 years (range 0.1 to 30.0).
• The authors' conclusion: The authors concluded that workers in asbestos cement, thermal insulation and shipbuilding industries were at significantly increased risks for malignant pleural mesothelioma. They recommended a national long-term surveillance system for early detection of asbestos-related diseases in Taiwan.
• Limitations the authors state:
  • No long-term data on airborne asbestos fibre levels, especially in the early period, so a job-exposure matrix could not be built.
  • Age adjustment was not practical because of the small number of cases in individual factories.
  • Underdiagnosis of mesothelioma, and diagnostic criteria that changed over time, may have led the study to underestimate risks.
  • The cohort did not include uninsured workers, such as temporary labourers, or employees of firms with fewer than five employees.
  • The authors had no information on environmental or non-occupational exposure of the cases.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Latency, Cancer Registry, rate ratio, Incidence, Asbestos-Cement, Thermal System Insulation (TSI).

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