title: Active smoking, passive smoking, and breast cancer risk: findings from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk.
abstract: BACKGROUND
  Evidence is lacking regarding the relationship between cigarette smoking and breast cancer in Japanese women. We examined the association between breast cancer incidence and active and passive smoking in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk.
  
  
  METHODS
  Our study comprised 34,401 women aged 40-79 years who had not been diagnosed previously with breast cancer and who provided information on smoking status at baseline (1988-1990). The subjects were followed from enrollment until December 31, 2001. Cox proportional-hazards models were used to estimate the hazard ratio (HR) and 95% confidence interval (CI) for the association between breast cancer incidence and tobacco smoke.
  
  
  RESULTS
  During 271,412 person-years of follow-up, we identified 208 incident cases of breast cancer. Active smoking did not increase the risk of breast cancer, with a HR for current smokers of 0.67 (95% CI: 0.32-1.38). Furthermore, an increased risk of breast cancer was not observed in current smokers who smoked a greater number of cigarettes each day. Overall, passive smoking at home or in public spaces was also not associated with an increased risk of breast cancer among nonsmokers. Women who reported passive smoking during childhood had a statistically insignificant increase in risk (HR: 1.24; 95% CI: 0.84-1.85), compared with those who had not been exposed during this time.
  
  
  CONCLUSIONS
  Smoking may not be associated with an increased risk of breast cancer in this cohort of Japanese women.
authors.affiliation: Department of Public Health, Aichi Medical University School of Medicine, Aichi, Japan.
authors.forename: Yingsong
authors.initials: Y
authors.lastname: Lin
authors.forename: Shogo
authors.initials: S
authors.lastname: Kikuchi
authors.forename: Koji
authors.initials: K
authors.lastname: Tamakoshi
authors.forename: Kenji
authors.initials: K
authors.lastname: Wakai
authors.forename: Takaaki
authors.initials: T
authors.lastname: Kondo
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Niwa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yatsuya
authors.forename: Kazuko
authors.initials: K
authors.lastname: Nishio
authors.forename: Sadao
authors.initials: S
authors.lastname: Suzuki
authors.forename: Shinkan
authors.initials: S
authors.lastname: Tokudome
authors.forename: Akio
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Hideaki
authors.initials: H
authors.lastname: Toyoshima
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Mori
authors.forename: Akiko
authors.initials: A
authors.lastname: Tamakoshi
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008875:Middle Aged; D016017:Odds Ratio; D011159:Population Surveillance; D016016:Proportional Hazards Models; D012107:Research Design; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D014028:Tobacco Smoke Pollution / Q000706:statistics & numerical data*; D016387:Women's Health
chemical_list: D014028:Tobacco Smoke Pollution