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Considerations of circadian impact for defining ‘shift work’ in cancer studies: IARC Working Group Report
  1. Richard G Stevens1,
  2. Johnni Hansen2,
  3. Giovanni Costa3,
  4. Erhard Haus4,
  5. Timo Kauppinen5,
  6. Kristan J Aronson6,
  7. Gemma Castaño-Vinyals7,
  8. Scott Davis8,
  9. Monique H W Frings-Dresen9,
  10. Lin Fritschi10,
  11. Manolis Kogevinas11,
  12. Kazutaka Kogi12,
  13. Jenny-Anne Lie13,
  14. Arne Lowden14,
  15. Beata Peplonska15,
  16. Beate Pesch16,
  17. Eero Pukkala17,
  18. Eva Schernhammer18,
  19. Ruth C Travis19,
  20. Roel Vermeulen20,
  21. Tongzhang Zheng21,
  22. Vincent Cogliano22,
  23. Kurt Straif22
  1. 1University of Connecticut Health Center, Farmington, Connecticut, USA
  2. 2Danish Cancer Society, Copenhagen, Denmark
  3. 3University of Milan, Milan, Italy
  4. 4University of Minnesota, HealthPartners Medical Group, St Paul, Minnesota, USA
  5. 5Finnish Institute of Occupational Health, Helsinki, Finland
  6. 6Queen's University, Ontario, Canada
  7. 7Centre for Research in Environmental Epidemiology (CREAL) and Municipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain
  8. 8Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
  9. 9Academic Medical Center (AMC) Amsterdam, Amsterdam, The Netherlands
  10. 10Western Australian Institute for Medical Research, University of Western Australia, Nedlands, Australia
  11. 11Municipal Institute of Medical Research (IMIM), Barcelona, Spain
  12. 12Institute for Science of Labour, Kawasaki, Japan
  13. 13National Institute of Occupational Health, Oslo, Norway
  14. 14Stockholm University, Stockholm, Sweden
  15. 15Nofer Institute of Occupational Medicine, Lodz, Poland
  16. 16Ruhr-University Bochum, Bochum, Germany
  17. 17Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Helsinki, Finland
  18. 18Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA
  19. 19Cancer Epidemiology Unit, University of Oxford, Oxford, UK
  20. 20University of Utrecht, Utrecht, The Netherlands
  21. 21Yale University School of Medicine, New Haven, Connecticut, USA
  22. 22International Agency for Research on Cancer, World Health Organization, Lyon, France
  1. Correspondence to Dr Richard G Stevens, University of Connecticut Health Center, Farmington, CT 06030, USA; bugs{at} or Kurt Straif, International Agency for Research on Cancer, World Health Organization, Lyon Cedex, France; straif{at}


Based on the idea that electric light at night might account for a portion of the high and rising risk of breast cancer worldwide, it was predicted long ago that women working a non-day shift would be at higher risk compared with day-working women. This hypothesis has been extended more recently to prostate cancer. On the basis of limited human evidence and sufficient evidence in experimental animals, in 2007 the International Agency for Research on Cancer (IARC) classified ‘shift work that involves circadian disruption’ as a probable human carcinogen, group 2A. A limitation of the epidemiological studies carried out to date is in the definition of ‘shift work.’ IARC convened a workshop in April 2009 to consider how ‘shift work’ should be assessed and what domains of occupational history need to be quantified for more valid studies of shift work and cancer in the future. The working group identified several major domains of non-day shifts and shift schedules that should be captured in future studies: (1) shift system (start time of shift, number of hours per day, rotating or permanent, speed and direction of a rotating system, regular or irregular); (2) years on a particular non-day shift schedule (and cumulative exposure to the shift system over the subject's working life); and (3) shift intensity (time off between successive work days on the shift schedule). The group also recognised that for further domains to be identified, more research needs to be conducted on the impact of various shift schedules and routines on physiological and circadian rhythms of workers in real-world environments.

  • Circadian disruption
  • cancer
  • shift work
  • epidemiology

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  • Funding The workshop was funded by the Health and Safety Executive (HSE), UK, and the German Social Accident Insurance (DGUV). The two sponsors were represented at the workshop by A Cassidy (HSE), F Jahn and FP Bochmann (DGUV).

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.