title: Active and passive smoking in breast cancer: prospective results from the Nurses' Health Study.
abstract: BACKGROUND
  The role of active and passive smoking in breast cancer remains controversial.
  
  
  METHODS
  Using data collected in the prospective Nurses' Health Study, we examined the influence of active and passive smoking on the incidence of invasive breast cancer. The analysis was based on women responding to the 1982 questionnaire, which included questions on passive smoking exposure. Information on active smoking was collected in biennial questionnaires. A total of 78,206 women were followed prospectively from 1982 until June 1996.
  
  
  RESULTS
  Of these women, 3,140 reported a diagnosis of invasive breast cancer during follow-up. Compared with never active smoking, relative risks (RR) of breast cancer were 1.04 (95% CI = 0.94-1.15) for current active smoking and 1.09 (95% CI = 1.00-1.18) for past active smoking. The RR for regular passive exposure at work and at home was 0.90 (95% CI = 0.67-1.22). For active smoking, a modest increase in risk was confined to women who began smoking before the age of 17 (RR = 1.19; 95% CI = 1.03-1.37).
  
  
  CONCLUSIONS
  Results suggest that passive smoking is unrelated to breast cancer. However, results for active smoking are compatible with a small increase in risk when smoking is initiated at young ages.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA. kegan@hsph.harvard.edu
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Egan
authors.forename: Meir J
authors.initials: MJ
authors.lastname: Stampfer
authors.forename: David
authors.initials: D
authors.lastname: Hunter
authors.forename: Susan
authors.initials: S
authors.lastname: Hankinson
authors.forename: Bernard A
authors.initials: BA
authors.lastname: Rosner
authors.forename: Michelle
authors.initials: M
authors.lastname: Holmes
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.forename: Graham A
authors.initials: GA
authors.lastname: Colditz
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015999:Multivariate Analysis; D009726:Nurses; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution