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0333 Night shift work and breast cancer risk: a combined analysis of population-based case-control studies with complete work histories
  1. Emilie Cordina-Duverger1,
  2. Florence Menegaux1,
  3. Aboubakari Nambiema1,
  4. Sylvia Rabstein2,
  5. Volker Harth3,
  6. Beate Pesch2,
  7. Thomas Brüning2,
  8. Lin Fritschi4,
  9. Deborah Glass5,
  10. Jane Heyworth6,
  11. Thomas Erren7,
  12. Gemma Castaño-Vinyals8,10,
  13. Kyriaki Papantoniou9,10,
  14. Ana Espinosa8,10,
  15. Manolis Kogevinas8,10,
  16. Anne Grundy13,
  17. John J Spinelli11,
  18. Kristan J Aronson12,
  19. Pascal Guenel1
  1. 1INSERM, CESP (UMRS 1018) Paris-Saclay University, Paris Sud University, Villejuif, France
  2. 2Research Institute of Occupational Medicine of the German Social Accident Insurance (BGFA), Ruhr University Bochum, Bochum, Germany
  3. 3Institute for Occupational and Maritime Medicine (ZfAM) , University Medical Centre Hamburg-Eppendorf (UKE), Hamburg, Germany
  4. 4Western Australian Institute for Medical Research, University of Western Australia, Perth, Australia
  5. 5Department of Epidemiology and Preventive Medicine, School of Public health and Preventive medicine. Monash University, Melbourne, Australia
  6. 6School of Population Health, The University of Western Australia, Nedlands, Australia
  7. 7Institute and Policlinic for Prevention Research, University of Cologne, Cologne, Germany
  8. 8ISGlobal, Centre for Research in Environmental Epidemiology, IMIM (Hospital del Mar Medical Research Institute), Barcelona, Spain
  9. 9Department of Epidemiology, Medical University of Vienna, Vienna, Austria
  10. 10Universitat Pompeu Fabra (UPF), Barcelona, CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain
  11. 11Department of Cancer Control Research, Cancer Agency; School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada
  12. 12Department of Public Health Sciences and Queen’s Cancer Research Institute, Queen’s University, Kingston, Ontario, Canada
  13. 13Department of Social and Preventive Medicine, Université de Montréal, Montreal, Canada

Abstract

In 2007, IARC classified ”shift work that involves circadian disruption” as probably carcinogenic to humans. To date, the evidence that night shift work increases the risk of breast cancer remains limited, partly because exposure to night work is defined differently across studies. To overcome this limitation, we created a single harmonised dataset using a common definition of night work from 5 major population-based case-control studies on breast cancer in Australia, Canada, France, Germany, and Spain.

The dataset included 6000 breast cancer cases and 7000 population controls. Any job held during work history that included at least 3 hours between midnight and 5 am was classified as night work. Lifetime duration of night work, frequency (nights/week), and night shift length (hours) were used as the main exposure variables.

In pre-menopausal women who ever worked at night the pooled OR was 1.23 [1.03–1.47]. The OR increased to 1.75 [1.17–2.62] in premenopausal women who worked at least 3 nights/week and 1.33 [1.05–1.70] for night shifts≥10 hours. The OR did not increase with the number of years of night work, but women who worked ≥3 nights/week for ≥10 years had an OR of 2.58 [1.05–6.36]. No association emerged from the data in post-menopausal women. No statistically significant heterogeneity between studies was observed.

Our results support the hypothesis that night work increases breast cancer risk, particularly in pre-menopausal who worked at least 3 nights per week. The absence of an association in post-menopausal women needs further scrutiny.

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