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Active smoking and secondhand smoke increase breast cancer risk: the report of the Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk (2009)
  1. Kenneth C Johnson1,
  2. Anthony B Miller2,
  3. Neil E Collishaw3,
  4. Julie R Palmer4,
  5. S Katharine Hammond5,
  6. Andrew G Salmon6,
  7. Kenneth P Cantor7,
  8. Mark D Miller8,9,
  9. Norman F Boyd10,
  10. John Millar11,
  11. Fernand Turcotte12
  1. 1Science Integration Division, Centre for Chronic Disease Prevention and Control, Public Health Agency of Canada, Ottawa, Ontario, Canada
  2. 2Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  3. 3Physicians for a Smoke-Free Canada, Ottawa, Ontario, Canada
  4. 4Boston University School of Public Health, Slone Epidemiology Center at Boston University, Boston, Massachusetts, USA
  5. 5School of Public Health, University of California, Berkeley, California, USA
  6. 6Air Toxicology and Risk Assessment Division, Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California, USA
  7. 7Division of Cancer Epidemiology and Genetics, US National Cancer Institute, Bethesda, Maryland, USA; currently of KP Cantor Environmental LLC, Silver Spring, Maryland, USA
  8. 8Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California, USA
  9. 9Paediatric Environmental Health Specialty Unit, University of California, San Francisco, California, USA
  10. 10The Campbell Family Institute for Breast Cancer Research, Ontario Cancer Institute, University of Toronto, Toronto, Ontario, Canada
  11. 11Population Health, Provincial Health Services Authority, Vancouver, British Columbia, Canada
  12. 12Département de médecine sociale et préventive, Université Laval, Québec City, Québec, Canada
  1. Correspondence to Kenneth C Johnson, Science Integration Division, Centre for Chronic Disease Prevention and Control, Public Health Agency of Canada, 785 Carling Avenue, Ottawa K1A 0K9, Canada; ken_lcdc_johnson{at}


Four authoritative reviews of active smoking and breast cancer have been published since 2000, but only one considered data after 2002 and conclusions varied. Three reviews of secondhand smoke (SHS) and breast cancer (2004–2006) each came to different conclusions. With 30 new studies since 2002, further review was deemed desirable. An Expert Panel was convened by four Canadian agencies, the Ontario Tobacco Research Unit, the Public Health Agency of Canada, Physicians for a Smoke-Free Canada and the Canadian Partnership Against Cancer to comprehensively examine the weight of evidence from epidemiological and toxicological studies and understanding of biological mechanisms regarding the relationship between tobacco smoke and breast cancer. This article summarises the panel's full report ( There are 20 known or suspected mammary carcinogens in tobacco smoke, and recognised biological mechanisms that explain how exposure to these carcinogens could lead to breast cancer. Results from the nine cohort studies reporting exposure metrics more detailed than ever/never and ex/current smoker show that early age of smoking commencement, higher pack-years and longer duration of smoking increase breast cancer risk 15% to 40%. Three meta-analyses report 35% to 50% increases in breast cancer risk for long-term smokers with N-acetyltransferase 2 gene (NAT2) slow acetylation genotypes. The active smoking evidence bolsters support for three meta-analyses that each reported about a 65% increase in premenopausal breast cancer risk among never smokers exposed to SHS. The Panel concluded that: 1) the association between active smoking and breast cancer is consistent with causality and 2) the association between SHS and breast cancer among younger, primarily premenopausal women who have never smoked is consistent with causality.

  • Environmental tobacco smoke
  • smoking caused disease

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  • Funding The Public Health Agency of Canada provided financial support for travel and accommodation to bring the Expert Panel together for their meeting in November 2008. The Ontario Tobacco Research Unit provided financial support of the Expert Panel by paying for the meeting space and funds for production and printing of the Expert Panel report. Views expressed in this report represent those of the panel members and do not necessarily represent the views of the respective institutions they work for.

  • Competing interests None to declare.

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