title: A pooled analysis of smoking and colorectal cancer: timing of exposure and interactions with environmental factors.
abstract: BACKGROUND
  Considerable evidence suggests that cigarette smoking is associated with a higher risk of colorectal cancer (CRC). What is unclear, however, is the impact of quitting smoking on risk attenuation and whether other risk factors for CRC modify this association.
  
  
  METHODS
  We conducted a pooled analysis of eight studies, including 6,796 CRC cases and 7,770 controls, to evaluate the association between cigarette smoking history and CRC risk and to investigate potential effect modification by other risk factors.
  
  
  RESULTS
  Current smokers [OR, 1.26; 95% confidence interval (CI), 1.11-1.43] and former smokers (OR, 1.18; 95% CI, 1.09-1.27), relative to never smokers, showed higher risks of CRC. Former smokers remained at higher CRC risk, relative to never smokers, for up to about 25 years after quitting. The impact of time since quitting varied by cancer subsite: The excess risk due to smoking decreased immediately after quitting for proximal colon and rectal cancer but not until about 20 years post-quitting for distal colon cancer. Furthermore, we observed borderline statistically significant additive interactions between smoking status and body mass index [BMI; relative excess risk due to interaction (RERI]), 0.15; 95% CI, -0.01 to 0.31; P = 0.06] and significant additive interaction between smoking status and fruit consumption (RERI, 0.16; 95% CI, 0.01-0.30; P = 0.04).
  
  
  CONCLUSIONS
  CRC risk remained increased for about 25 years after quitting smoking, and the pattern of decline in risk varied by cancer subsite. BMI and fruit intake modified the risk associated with smoking.
  
  
  CONCLUSIONS
  These results contribute to a better understanding of the mechanisms through which smoking impacts CRC etiology.
authors.affiliation: Public Health Sciences Division, Fred Hutchinson Cancer Research Center, University of Washington, Seattle, WA 98109, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Gong
authors.forename: Carolyn
authors.initials: C
authors.lastname: Hutter
authors.forename: John A
authors.initials: JA
authors.lastname: Baron
authors.forename: Sonja
authors.initials: S
authors.lastname: Berndt
authors.forename: Bette
authors.initials: B
authors.lastname: Caan
authors.forename: Peter T
authors.initials: PT
authors.lastname: Campbell
authors.forename: Graham
authors.initials: G
authors.lastname: Casey
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Chan
authors.forename: Michelle
authors.initials: M
authors.lastname: Cotterchio
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fuchs
authors.forename: Steven
authors.initials: S
authors.lastname: Gallinger
authors.forename: Edward
authors.initials: E
authors.lastname: Giovannucci
authors.forename: Tabitha
authors.initials: T
authors.lastname: Harrison
authors.forename: Richard
authors.initials: R
authors.lastname: Hayes
authors.forename: Li
authors.initials: L
authors.lastname: Hsu
authors.forename: Shuo
authors.initials: S
authors.lastname: Jiao
authors.forename: Yi
authors.initials: Y
authors.lastname: Lin
authors.forename: Noralane M
authors.initials: NM
authors.lastname: Lindor
authors.forename: Polly
authors.initials: P
authors.lastname: Newcomb
authors.forename: Bethann
authors.initials: B
authors.lastname: Pflugeisen
authors.forename: Amanda I
authors.initials: AI
authors.lastname: Phipps
authors.forename: Thomas
authors.initials: T
authors.lastname: Rohan
authors.forename: Robert
authors.initials: R
authors.lastname: Schoen
authors.forename: Daniela
authors.initials: D
authors.lastname: Seminara
authors.forename: Martha L
authors.initials: ML
authors.lastname: Slattery
authors.forename: Deanna
authors.initials: D
authors.lastname: Stelling
authors.forename: Fridtjof
authors.initials: F
authors.lastname: Thomas
authors.forename: Greg
authors.initials: G
authors.lastname: Warnick
authors.forename: Emily
authors.initials: E
authors.lastname: White
authors.forename: John
authors.initials: J
authors.lastname: Potter
authors.forename: Ulrike
authors.initials: U
authors.lastname: Peters
mesh_terms: D000328:Adult; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006801:Humans; D008019:Life Style; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects / Q000453:epidemiology*; D013997:Time Factors; D014481:United States / Q000453:epidemiology