Cancer Incidence in Asbestos-Exposed Workers: An Update on Four Finnish Cohorts

Our plain-English summary of Cancer Incidence in Asbestos-Exposed Workers: An Update on Four Finnish Cohorts, by P. Nynäs, E. Pukkala, H. Vainio, et al (Safety and Health at Work, 2017).

The study

• Authors: P. Nynäs, E. Pukkala, H. Vainio, P. Oksa
• Journal: Safety and Health at Work
• Published: 2017;8(2):169-174
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: We assessed the cancer risks of four different Finnish asbestos-exposed cohorts. We also explored if the cohorts with varying profiles of asbestos exposure exhibited varying relative risks of cancer.

Methods: The incident cancer cases for the asbestos-exposed worker cohorts were updated to the end of 2012 using the files of the Finnish Cancer Registry. The previously formed cohorts consisted of asbestos mine workers, asbestosis patients, asbestos sprayers, and workers who had taken part in a screening study based on asbestos exposure at work.

Results: The standardized incidence ratio (SIR) for mesothelioma varied from about threefold to > 100-fold in the different cohorts. In the screening cohort the SIR for mesothelioma was highest in 2003-2007, In other cohorts it was more constant in 5-year period inspection. The SIR for lung cancer was about twofold to tenfold in all except the screening cohort. Asbestos sprayers were at the highest risk of mesothelioma and lung cancer.

Conclusion: The SIR for mesothelioma is high in all of the cohorts that represent different kinds of asbestos exposure. The smaller SIR for mesothelioma in the screening cohort with lowest level of asbestos exposure might suggest dose-responsiveness between asbestos exposure and mesothelioma. It does seem that the highest risk of lung cancer in these cohorts except in the youngest of the cohorts, the screening cohort, is over. The highest SIR for lung cancer of the asbestosis patient and sprayers cohort is explained by their heavy asbestos exposure.

In plain English

This study updated cancer incidence to the end of 2012 in four Finnish asbestos-exposed cohorts, comparing observed cancers with numbers expected from Finnish population rates (standardized incidence ratios, SIRs). The cohorts were 734 anthophyllite mine workers, 128 asbestosis patients, 133 crocidolite sprayers and 24,214 screening-campaign workers, mostly in construction. There were 108 mesotheliomas in all. The mesothelioma SIR was 127 (95% CI 63.3 to 226) among sprayers, 49.6 (16.1 to 115) among asbestosis patients, 13.2 (5.70 to 26.0) among mine workers and 2.95 (2.35 to 3.65) in the screening cohort. Lung cancer SIRs were 11.3 (7.10 to 17.2), 8.19 (5.88 to 11.1), 2.46 (1.95 to 3.07) and 1.23 (1.16 to 1.30) in the same groups. Lung cancer SIRs seemed to have fallen since the late 1990s except in the screening cohort. The authors found no increased risk of ovarian or laryngeal cancer. They concluded that the screening cohort's smaller mesothelioma SIR would suggest a dose-response, and that the highest lung cancer risk in the older cohorts seemed over. Smoking habits after cohort formation were unknown, the authors noted.

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: Cohort study: an updated cancer-incidence follow-up of four previously formed asbestos-exposed cohorts, linked to the Finnish Cancer Registry. Observed cancers were compared with numbers expected from Finnish population rates (standardized incidence ratios).
• Who was studied: Four Finnish cohorts followed to December 31, 2012. (1) 734 workers employed at least 3 months between January 1953 and July 1967 at the Paakkila and Maljasalmi anthophyllite asbestos mines. (2) 128 asbestosis patients examined at the Finnish Institute of Occupational Health; this cohort was formed in 1977 to 1985. (3) 133 asbestos sprayers identified in 1987; 3 men were excluded for missing identification data. (4) 24,214 workers from an asbestos screening campaign in 1990 to 1992; 71% were construction workers.
• Exposure: Mine workers were exposed to anthophyllite asbestos. Sprayers were exposed to crocidolite; spraying in Finland took place from 1955 to 1976. The asbestosis patients had worked in insulation, asbestos mines, asbestos cement factories, spraying or other asbestos work, with a mean exposure of 21 years (range 4 to 40). The screening cohort had a mean of 26 years of asbestos-exposing work and mixed exposures, mainly in construction. Asbestos cement in Finland contained chrysotile.
• Main results:
  • 108 mesotheliomas occurred during follow-up across the four cohorts.
  • Asbestos sprayers: 11 mesotheliomas, SIR 127 (95% CI 63.3 to 226).
  • Asbestosis patients: 5 mesotheliomas, SIR 49.6 (95% CI 16.1 to 115).
  • Asbestos mine workers: 8 mesotheliomas, SIR 13.2 (95% CI 5.70 to 26.0).
  • Screening cohort: 84 mesotheliomas, SIR 2.95 (95% CI 2.35 to 3.65).
  • In the screening cohort the mesothelioma SIR was highest in 2003 to 2007: 37 cases, SIR 4.69 (95% CI 3.30 to 6.45).
  • A total of 1,135 lung cancers were observed among men and women in the four cohorts.
  • Asbestos sprayers, all smoking categories: 22 lung cancers, SIR 11.3 (95% CI 7.10 to 17.2).
  • Asbestosis patients, all smoking categories: 41 lung cancers, SIR 8.19 (95% CI 5.88 to 11.1).
  • Asbestos mine workers, all smoking categories: 78 lung cancers, SIR 2.46 (95% CI 1.95 to 3.07).
  • Screening cohort: 994 lung cancers, SIR 1.23 (95% CI 1.16 to 1.30).
  • Looking at 5-year periods, lung cancer SIRs seemed to have diminished since the late 1990s in all cohorts except the screening cohort.
  • The highest lung cancer SIRs were among smokers in each exposure group, except in the asbestos sprayer cohort.
  • Laryngeal cancer in the screening cohort: 3 cases among nonsmokers (SIR 0.26, 95% CI 0.05 to 0.77), 34 among smokers (SIR 1.31, 95% CI 0.90 to 1.82) and 15 among those with unknown smoking status (SIR 1.40, 95% CI 0.78 to 2.31). Only one case occurred in the other cohorts.
  • Six ovarian cancers were observed, all in the screening cohort: 4 among nonsmokers (SIR 1.14, 95% CI 0.31 to 2.92) and 2 among smokers (SIR 1.02, 95% CI 0.12 to 3.67). The authors found no increased risk of ovarian or laryngeal cancer.
• The authors' conclusion: The authors concluded the following. Mesothelioma SIRs were high, but the number of cases per year was small. Sprayers exposed to crocidolite had the highest mesothelioma and lung cancer risk. The smaller mesothelioma SIR in the screening cohort would suggest dose-responsiveness. The highest lung cancer risk in the older cohorts seemed to be over, but it remained elevated in the screening cohort. They attributed the high lung cancer SIRs of the asbestosis patients and sprayers to heavy asbestos exposure.
• Limitations the authors state:
  • Smoking habits after the cohorts were formed were unknown, so smokers and ex-smokers were analyzed together.
  • The cohorts differed in when exposure began and ended, and mesothelioma latency varies widely. The authors said this made it impossible to conclude when mesothelioma risk starts to diminish after exposure ends.
  • The authors said it is unclear whether the level of asbestos exposure affected mesothelioma risk.
  • The total number of women was small (1,091), which limits the ovarian cancer findings.
  • Overall SIRs of the different cohorts are not directly comparable if their age and calendar-period distributions differ.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Relative Risk, Cancer Registry, Standardized Incidence Ratio (SIR), Mesothelioma, Lung Cancer.

Related studies

• Four cases of mesothelioma among Finnish anthophyllite miners — A. Karjalainen, L.O. Meurman, et al. (1994)
• Cancer incidence and mortality among Finnish asbestos sprayers and in asbestosis and silicosis patients — P. Oksa, E. Pukkala, et al. (1997)
• Update of mortality and cancer incidence in the Australian petroleum industry cohort — R.T. Gun, N. Pratt, et al. (2006)
• Past exposure to asbestos and combustion products and incidence of cancer among Finnish locomotive drivers — P. Nokso-Koivisto, E. Pukkala (1994)
• Incidence of cancer among Finnish patients with asbestos-related pulmonary or pleural fibrosis — A. Karjalainen, E. Pukkala, et al. (1999)
• Tyler asbestos workers: A mortality update in a cohort exposed to amosite — J.L. Levin, A. Rouk, et al. (2016)

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