Cancer and non-cancer mortality among French uranium cycle workers: the TRACY cohort

Our plain-English summary of Cancer and non-cancer mortality among French uranium cycle workers: the TRACY cohort, by E. Samson, I. Piot, S. Zhivin, et al (BMJ Open, 2016).

The study

• Authors: E. Samson, I. Piot, S. Zhivin, D.B. Richardson, P. Laroche, A.P. Serond, D. Laurier, O. Laurent
• Journal: BMJ Open
• Published: 2016;6(4):e010316
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: The health effects of internal contamination by radionuclides, and notably by uranium, are poorly characterised. New cohorts of uranium workers are needed to better examine these effects. This paper analyses for the first time the mortality profile of the French cohort of uranium cycle workers. It considers mortality from cancer and non-cancer causes.

Methods: The cohort includes workers employed at least 6 months between 1958 and 2006 in French companies involved in the production of nuclear fuel. Vital status and causes of death were collected from French national registries. Workers were followed-up from 1 January 1968 to 31 December 2008. Standardised mortality ratios (SMRs) were computed based on mortality rates for the French general population.

Results: The cohort includes 12,649 workers (88% men). The average length of follow-up is 27 years and the mean age at the end of the study is 60 years. Large mortality deficits are observed for non-cancer causes of death such as non-cancer respiratory diseases (SMR=0.51 (0.41 to 0.63)) and circulatory diseases (SMR=0.68 (0.62 to 0.74)). A mortality deficit of lower magnitude is also observed for all cancers combined (SMR (95% CI): 0.76 (0.71 to 0.81)). Pleural mesothelioma is elevated (SMR=2.04 (1.19 to 3.27)).

Conclusions: A healthy worker effect is observed in this new cohort of workers involved in the uranium cycle. Collection of individual information on internal uranium exposure as well as other risk factors is underway, to allow for the investigation of uranium-related risks.

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In plain English

This retrospective cohort study followed 12,649 people (88% men) who had worked at least 6 months on the permanent staff of French nuclear fuel production companies between 1958 and 2006. Their deaths from 1968 to 2008 were compared with those expected from French general-population rates. Individual uranium exposure had not yet been reconstructed. Overall, the workers died less often than expected from all causes (standardised mortality ratio, SMR, 0.65; 95% CI 0.62 to 0.68; 2130 deaths) and from all cancers (SMR 0.76; 0.71 to 0.81). The authors described this as a healthy worker effect. Pleural mesothelioma, however, showed a statistically significant excess, which the authors called twofold: 17 deaths, SMR 2.04 (95% CI 1.19 to 3.27). Several other cancers, including pancreas, skin melanoma, and brain and central nervous system cancer, had higher-than-expected figures that were not statistically significant. The authors noted that asbestos exposure, a strong risk factor for mesothelioma, was known to have occurred in companies in the cohort and might contribute to the excess. They also acknowledged that mesothelioma recording on death certificates was problematic until at least the early 1990s.

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: retrospective cohort study comparing workers' mortality with the French general population (standardised mortality ratios)
• Who was studied: 12,649 workers (88% men) on the permanent staff for at least 6 months, between 1958 and 2006, of French companies in the nuclear fuel production cycle; deaths followed from 1 January 1968 to 31 December 2008
• Exposure: employment in French uranium fuel cycle companies (purification of natural uranium, conversion to uranium hexafluoride, enrichment by gaseous diffusion, fuel manufacturing, storage and decontamination); individual uranium exposure was not yet reconstructed, and asbestos exposure was not measured in this analysis
• Main results:
  • Whole cohort, all causes of death: SMR 0.65 (95% CI 0.62 to 0.68), 2130 deaths
  • Whole cohort, all cancers: SMR 0.76 (95% CI 0.71 to 0.81), 912 deaths
  • Whole cohort, pleural mesothelioma: SMR 2.04 (95% CI 1.19 to 3.27), 17 deaths
  • Whole cohort, non-significant excesses for other cancers, including pancreas (SMR 1.05; 95% CI 0.79 to 1.38; 53 deaths)
  • Whole cohort, skin melanoma: SMR 1.60 (95% CI 0.90 to 2.64), 15 deaths, not significant
  • Whole cohort, brain and central nervous system cancer: SMR 1.36 (95% CI 0.93 to 1.91), 32 deaths, not significant
  • Whole cohort, lung cancer: 217 deaths, SMR 0.73 (95% CI 0.64 to 0.83)
  • Whole cohort, non-malignant respiratory diseases: SMR 0.51 (95% CI 0.41 to 0.63), 88 deaths; circulatory diseases: SMR 0.68 (95% CI 0.62 to 0.74), 540 deaths
  • Whole cohort, smoking-related cancers: SMR 0.68 (95% CI 0.62 to 0.75), 495 deaths
  • Among workers 20 or more years after the end of employment, cancer mortality was not significantly different from the general population (SMR 0.89; 95% CI 0.79 to 1.02)
  • The authors interpreted the overall mortality deficits as a healthy worker effect
• The authors' conclusion: The authors concluded that mortality was lower than in the general population for all broad groups of causes, consistent with a healthy worker effect. They found that malignant pleural mesothelioma was significantly in excess, with non-significant excesses for a few other cancer sites. They suggested that asbestos exposure, known to have occurred in companies included in the cohort, might contribute to the mesothelioma excess.
• Limitations the authors state:
  • No individual cause-of-death data were available in France before 1968
  • Diagnosis and recording of mesothelioma on death certificates was problematic until at least the early 1990s
  • Some workers not exposed to uranium are included, and exposed and non-exposed workers cannot yet be separated
  • Mortality data do not capture diseases that are rarely fatal
  • Contractors could not be included
  • Statistical power to study rare or specific diseases is limited

Topics

The National Library of Medicine indexes this study under subjects our site covers: Power plants and utilities.

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Healthy Worker Effect.

Related studies

• French cohort of the uranium processing workers: mortality pattern after 30-year follow-up — I. Guseva Canu, E. Cardis, et al. (2010)
• Impact of chemical exposure on cancer mortality in a French cohort of uranium processing workers — S. Zhivin, D. Laurier, et al. (2013)
• Comparative assessing for radiological, chemical, and physical exposures at the French uranium conversion plant: Is uranium the only stressor? — I. Guseva Canu, F. Paquet, et al. (2009)
• Mortality of older construction and craft workers employed at department of energy (DOE) nuclear sites: follow-up through 2011 — K. Ringen, J. Dement, et al. (2015)
• Exposure assessment for a cohort of workers at a former uranium processing facility — J.L. Anderson, R.D. Daniels, et al. (2012)
• Mortality of workers in a French asbestos cement factory 1940-82 — A.M. Alies-Patin, A.J. Valleron (1985)

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