title: Tobacco smoking and colorectal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population.
abstract: BACKGROUND
  It is unclear whether tobacco smoking is related to colorectal cancer risk in Japan. We evaluated the association among the Japanese population based on a systematic review of epidemiologic evidence.
  
  
  METHODS
  Original data were obtained from searches of MEDLINE using PubMed, complemented with manual searches. The 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
  A total of six cohort studies and 15 case-control studies were thus identified. A substantial degree of heterogeneity was observed in the association between smoking and colon cancer; most case-control studies published before 1994 reported an inverse association, whereas studies conducted over the last decade did not find any significant association. Recent cohort studies have shown a non-significant 20-40% increase in colon cancer risk associated with current smoking. Several recent case-control studies and some cohort studies have identified a weak to strong positive association between smoking and rectal cancer.
  
  
  CONCLUSIONS
  We conclude that tobacco smoking possibly increases the risk of colorectal cancer among the Japanese population. More specifically, tobacco smoking may possibly increase the risk of rectal cancer; however, epidemiologic evidence is still insufficient to demonstrate any clear association with colon cancer.
authors.affiliation: Department of Preventive Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan. mizoue@phealth.med.kyushu-u.ac.jp
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Mizoue
authors.forename: Manami
authors.initials: M
authors.lastname: Inoue
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: Chisato
authors.initials: C
authors.lastname: Nagata
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D000428:Alcohol Drinking / Q000009:adverse effects; D016022:Case-Control Studies; D015331:Cohort Studies; D003110:Colonic Neoplasms / Q000453:epidemiology* / Q000209:etiology; D004032:Diet; D005260:Female; D006184:Habits; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008019:Life Style; D008297:Male; D012004:Rectal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D012306:Risk; D012907:Smoking / Q000009:adverse effects*