title: Tobacco smoking and breast cancer risk: an evaluation based on a systematic review of epidemiological evidence among the Japanese population.
abstract: BACKGROUND
  Our research group undertook an appraisal of the body of epidemiological studies on cancer in Japan to evaluate the existing evidence concerning the association between health-related lifestyles and cancer. As tobacco smoking may be one of the few modifiable risk factors for breast cancer, we focused on the association between tobacco smoking and the risk of breast cancer in this review.
  
  
  METHODS
  A MEDLINE search was conducted to identify epidemiological studies on the association between smoking and breast cancer incidence or mortality among the Japanese from 1966 to 2005. Evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer.
  
  
  RESULTS
  Three cohort studies and eight case-control studies were identified. The relative risk (RR) or odds ratio (OR) of breast cancer for current smokers ranged from 0.71 to 6.26 in these studies. A significantly increased risk among current smokers compared with never smokers (RR = 1.7) was reported in one out of the three cohort studies. Moderate or strong associations between smoking and breast cancer risk (OR > 2.0) were observed in four of the eight case-control studies. Experimental studies have supported the biological plausibility of a positive association between tobacco smoking and breast cancer risk.
  
  
  CONCLUSIONS
  We conclude that tobacco smoking possibly increases the risk of breast cancer in the Japanese population.
authors.affiliation: Department of Epidemiology & Preventive Medicine, Gifu University Graduate School of Medicine, Gifu, Japan. chisato@cc.gifu-u.ac.jp
authors.forename: Chisato
authors.initials: C
authors.lastname: Nagata
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mizoue
authors.forename: Keitaro
authors.initials: K
authors.lastname: Tanaka
authors.forename: Ichiro
authors.initials: I
authors.lastname: Tsuji
authors.forename: Kenji
authors.initials: K
authors.lastname: Wakai
authors.forename: Manami
authors.initials: M
authors.lastname: Inoue
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D044466:Asian People / Q000706:statistics & numerical data; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D016022:Case-Control Studies; D015331:Cohort Studies; D005069:Evaluation Studies as Topic; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008019:Life Style; D015337:Multicenter Studies as Topic; D016017:Odds Ratio; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology