Role of stopping exposure and recent exposure to asbestos in the risk of mesothelioma

Our plain-English summary of Role of stopping exposure and recent exposure to asbestos in the risk of mesothelioma, by C. La Vecchia, P. Boffetta (European Journal of Cancer Prevention, 2012).

The study

• Authors: C. La Vecchia, P. Boffetta
• Journal: European Journal of Cancer Prevention
• Published: 2012;21(3):227-30
• Type of article: Review
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The model of asbestos-related mesothelioma implies that the time since first exposure (latency) is the key determinant of subsequent risk. The role of recent exposure or stopping asbestos exposure, if any, is, however, open to discussion. A literature review was conducted to the end of 2010. In a cohort of 1966 Italian textile workers, the standardized mortality ratio, on the basis of 68 deaths from mesothelioma, was 6627 for workers employed only under the age of 30 years, 8019 for those employed both under the age of 30 years and at the age of 30-39 years, and 5891 for those employed both under the age of 30 years and at the age of 40 years or more. In a cohort of Italian asbestos cement workers, including 135 deaths from pleural cancer, compared with workers who had stopped exposure for 3-15 years, the relative risk (RR) was similar for those still employed (RR=0.67) and for those who had stopped for 30 years or more (RR=0.65). In a British case-control study, including 622 cases of mesothelioma and 1420 population controls, the RR substantially increased with increasing duration of exposure under the age of 30 years, but not with exposure at the age of more than 30 years. In the Great Britain Asbestos Workers Survey, including 649 deaths from mesothelioma compared with workers who were still employed and or had stopped for less than 10 years, the multivariate RRs were 0.90 10-20 years after stopping exposure and 0.99 both 20-30 and more than 30 years after stopping. There is consistent evidence showing that, for workers exposed in the distant past, the risk of mesothelioma is not appreciably modified by subsequent exposures, and that stopping exposure does not materially modify the subsequent risk of mesothelioma.

In plain English

This was a review article. The authors reviewed studies, to the end of 2010, on whether stopping exposure or recent exposure to asbestos changes later mesothelioma risk. They described two small studies, of Italian miners and German former asbestos workers, as giving little information. A cohort of 1,966 Italian asbestos textile workers had 68 mesothelioma deaths. Compared with national rates, the standardized mortality ratio was 6627 (95% CI 4287.5–9807.5) for those employed only under age 30, 8019 (3672.7–15236.1) for those also employed at 30–39, and 5896 (2163.8–12853.3) for those also employed at 40 or over. In 3,434 Italian asbestos cement workers, the authors reported no relation between time since last exposure and pleural cancer risk. A British case–control study found risk rose with years of exposure before age 30, while exposure after age 30 changed it only slightly and not significantly. In the Great Britain Asbestos Workers Survey, mesothelioma risk showed no tendency to fall with time since stopping exposure. The authors concluded that, for workers exposed long ago, later exposure and stopping exposure did not appreciably change mesothelioma risk.

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: Review article: a literature review of published studies to the end of 2010
• Who was studied: Studies reviewed: a cohort of 1,966 Italian asbestos textile workers (889 men, 1077 women) employed 1946–1984 and followed to 2004; 3,434 asbestos cement workers in northern Italy; a British nationwide case–control study of 622 mesothelioma patients registered 2001–2006 and 1420 population controls; the Great Britain Asbestos Workers Survey of over 98,000 workers; plus two small studies (1056 men from the Balangero mine in Italy; 576 male former asbestos workers in Germany)
• Exposure: Occupational asbestos exposure in textile work, asbestos cement production, mining and other jobs, analysed by age at exposure, duration of exposure and time since last exposure. The authors did not specify fiber types in the body of the review.
• Main results:
  • In the Italian asbestos textile cohort there were 68 deaths from mesothelioma: 39 pleural and 29 peritoneal, with an overall SMR of 4159.
  • In the Italian asbestos textile cohort, the mesothelioma SMR was 6627 for workers employed only under age 30, 8019 for those also employed at 30–39, and 5896 for those also employed at 40 or over. The authors described this as no effect of later exposure once exposure had occurred at a young age.
  • Table 1 gave wide 95% confidence intervals for these textile-cohort mesothelioma SMRs. The interval was 4287.5–9807.5 for first and last employment under age 30 (25 deaths). It was 3672.7–15236.1 for last employment at 30–39 (9 deaths) and 2163.8–12853.3 for last employment over 40 (6 deaths).
  • In the same textile cohort, lung cancer behaved differently: the SMR was 226 for workers employed below age 30 only, compared with 565 for those employed both at age 30 or less and at 40 or over.
  • In the Italian asbestos cement cohort (135 pleural cancer deaths), the reference group was workers who had stopped exposure 3–15 years earlier. The relative risk was 0.67 (95% CI 0.32–1.40) for workers still employed or who had stopped less than 3 years earlier. It was 0.65 (95% CI 0.26–1.63) for workers who had stopped 30 or more years earlier.
  • In the British case–control study, risk was compared with patients who had no occupational exposure. Among patients with less than 10 years of exposure after age 30, the relative risk was 3.9 (95% CI 2.2–6.8) for less than 10 years of exposure below age 30. It was 11.5 (95% CI 6.9–19.1) for 10 years or more of exposure below age 30.
  • In the British case–control study, exposure above age 30 changed the risk only slightly and not significantly: from 3.9 to 4.7 in one group and from 11.5 to 13.1 in the other.
  • In the Great Britain Asbestos Workers Survey (649 mesothelioma deaths), the reference group was workers who had stopped exposure less than 10 years earlier or were still employed. The multivariate relative risk of mesothelioma was 0.90 (95% CI 0.76–1.08) at 10–20 years after stopping and 0.99 (95% CI 0.78–1.26) at 20–30 years. It was 0.99 (95% CI 0.14–7.02, based on 1 case) at more than 30 years.
  • In the same survey, the relative risk of asbestosis was 0.68 (95% CI 0.51–0.92) for 20 years or more since stopping exposure, compared with less than 10 years or currently employed.
• The authors' conclusion: The authors concluded that, for workers exposed in the distant past, mesothelioma risk is not appreciably modified by later exposures. They also concluded that stopping exposure does not materially modify the later risk. They gave this as the reason for the still-expanding mesothelioma epidemic in Europe.
• Limitations the authors state:
  • The authors said two of the reviewed studies had only small numbers of mesothelioma cases and gave little information.
  • For the Italian mine study (5 mesothelioma deaths), the authors noted that none of the estimates was significant. The small numbers also did not allow adjustment for latency.
  • For the German study (15 pleural cancer deaths), the authors judged the multivariate results not interpretable because the model probably had too many variables for so few cases.
  • The authors noted that earlier data from the Rochdale asbestos textile factory were too limited to distinguish no effect from a limited effect of stopping exposure.

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, Latency, Asbestos Exposure, standardized mortality ratio (SMR), Asbestos-Cement, Relative Risk, Case-Control Study.

Related studies

• The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping beta-carotene and retinol supplements — G.E. Goodman, M.D. Thornquist, et al. (2004)
• Impact of occupational carcinogens on lung cancer risk in a general population — S. De Matteis, D. Consonni, et al. (2012)
• A critique of a review on the relationship between asbestos exposure and the risk of mesothelioma: reply — C. La Vecchia, P. Boffetta (2014)
• Recent mortality from pleural mesothelioma, historical patterns of asbestos use, and adoption of bans: a global assessment — K. Nishikawa, K. Takahashi, et al. (2008)
• Kidney cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies — D. Sali, P. Boffetta (2000)
• Increased risk of malignant mesothelioma of the pleura after residential or domestic exposure to asbestos: a case-control study in Casale Monferrato, Italy — C. Magnani, P. Dalmasso, et al. (2001)

Browse more research in European Journal of Cancer Prevention, or return to medical research.