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Association of active and passive smoking with risk of breast cancer among postmenopausal women: a prospective cohort study

BMJ 2011; 342 doi: (Published 01 March 2011) Cite this as: BMJ 2011;342:d1016
  1. Juhua Luo, assistant professor1,
  2. Karen L Margolis, senior clinical investigator2,
  3. Jean Wactawski-Wende, professor and associate chair3,
  4. Kimberly Horn, associate professor1, associate center director4,
  5. Catherine Messina, research associate professor 5,
  6. Marcia L Stefanick, professor6,
  7. Hilary A Tindle, assistant professor of medicine7,
  8. Elisa Tong, assistant professor8,
  9. Thomas E Rohan, professor9
  1. 1Department of Community Medicine, Mary Babb Randolph Cancer Center, West Virginia University, Morgantown, WV, USA
  2. 2HealthPartners Research Foundation, Box 1524, Mailstop 21111R, Minneapolis, MN 55440-1524, USA
  3. 3Department of Social and Preventive Medicine, University at Buffalo, Buffalo, NY, USA
  4. 4WV Prevention Research Center, West Virginia University
  5. 5Department of Preventive Medicine, Stony Brook University, NY, USA
  6. 6Stanford University School of Medicine, CA, USA
  7. 7Center for Research on Health Care, Division of General Internal Medicine, University of Pittsburgh, Pittsburgh, PA, USA
  8. 8Division of General Internal Medicine, University of California, Davis Medical Center, Sacramento, CA, USA
  9. 9Department of Epidemiology & Population Health, Albert Einstein College of Medicine, Bronx, NY, USA
  1. Corresponding to: K L Margolis Karen.L.Margolis{at}
  • Accepted 11 January 2011


Objective To examine the association between smoking and risk of invasive breast cancer using quantitative measures of lifetime passive and active smoking exposure among postmenopausal women.

Design Prospective cohort study.

Setting 40 clinical centres in the United States.

Participants 79 990 women aged 50–79 enrolled in the Women’s Health Initiative Observational Study during 1993–8.

Main outcome measures Self reported active and passive smoking, pathologically confirmed invasive breast cancer.

Results In total, 3520 incident cases of invasive breast cancer were identified during an average of 10.3 years of follow-up. Compared with women who had never smoked, breast cancer risk was elevated by 9% among former smokers (hazard ratio 1.09 (95% CI 1.02 to 1.17)) and by 16% among current smokers (hazard ratio 1.16 (1.00 to 1.34)). Significantly higher breast cancer risk was observed in active smokers with high intensity and duration of smoking, as well as with initiation of smoking in the teenage years. The highest breast cancer risk was found among women who had smoked for ≥50 years or more (hazard ratio 1.35 (1.03 to1.77) compared with all lifetime non-smokers, hazard ratio 1.45 (1.06 to 1.98) compared with lifetime non-smokers with no exposure to passive smoking). An increased risk of breast cancer persisted for up to 20 years after smoking cessation. Among women who had never smoked, after adjustment for potential confounders, those with the most extensive exposure to passive smoking (≥10 years’ exposure in childhood, ≥20 years’ exposure as an adult at home, and ≥10 years’ exposure as an adult at work) had a 32% excess risk of breast cancer compared with those who had never been exposed to passive smoking (hazard ratio 1.32 (1.04 to 1.67)). However, there was no significant association in the other groups with lower exposure and no clear dose response to cumulative passive smoking exposure.

Conclusions Active smoking was associated with an increase in breast cancer risk among postmenopausal women. There was also a suggestion of an association between passive smoking and increased risk of breast cancer.


  • Funding: The Women’s Health Initiative is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, US Department of Health and Human Services (contracts N01WH22110, 24152, 32100-2, 32105-6, 32108-9, 32111-13, 32115, 32118-32119, 32122, 42107-26, 42129-32, and 44221). The funding source had no role in the collection, analysis, or interpretation of the data, in the preparation of the manuscript, or its submission for publication.

  • Contributors: JL, KLM, and JWW participated in the study design. JL completed the data analysis. All authors participated in data collection, data interpretation, and drafting the manuscript. KLM is guarantor for the study.

  • Competing interests: All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare: support from the National Heart, Lung, and Blood Institute for the submitted work as described above; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: This study was approved by the ethics committees at the Women’s Health Initiative Coordinating Center, Fred Hutchinson Cancer Research Center, and at all 40 clinical centres.

  • Data sharing: No additional data available.

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