title: Risk of colorectal cancer associated with active smoking among female teachers.
abstract: OBJECTIVE
  The objective of this study was to examine the risk of colorectal cancer associated with active smoking among members of the California Teachers Study (CTS), a large cohort of female public school employees for whom highly detailed smoking information is available.
  
  
  METHODS
  The analysis was conducted among the 122,264 CTS participants who lived in California at cohort entry in 1995/1996, had no prior history of colorectal cancer, and provided detailed smoking information. 1,205 cases of invasive colorectal cancer prospectively diagnosed in 1995-2009 were identified from the California Cancer Registry, including 650 in the proximal colon, 267 in the distal colon, and 288 in the rectum. Hazard ratios and 95% confidence intervals were estimated using Cox proportional hazards models, stratified by age at cohort entry, and adjusted for race/ethnicity.
  
  
  RESULTS
  Compared to never smokers, current smokers had an approximately 30% increased risk of colorectal cancer. Overall, a slightly elevated risk was also noted for former smokers. Among former smokers, risks appeared to remain elevated for up to 20 years following cessation. Risks among former and current smokers increased with greater intensity and duration of smoking. Little evidence for heterogeneity in risk was noted for colon versus rectal cancer or for different subsites within the colon.
  
  
  CONCLUSIONS
  These results provide convincing evidence that heavy and/or long-term smoking is a risk factor for cancers of the colon and rectum. Such evidence should be considered when updating screening guidelines to include targeting people with long active smoking histories.
authors.affiliation: Cancer Prevention Institute of California, Berkeley, CA 94704, USA. susan.hurley@cpic.org
authors.forename: Susan
authors.initials: S
authors.lastname: Hurley
authors.forename: Debbie
authors.initials: D
authors.lastname: Goldberg
authors.forename: David O
authors.initials: DO
authors.lastname: Nelson
authors.forename: Yani
authors.initials: Y
authors.lastname: Lu
authors.forename: Katherine
authors.initials: K
authors.lastname: Henderson
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D016001:Confidence Intervals; D005178:Faculty; D005260:Female; D006801:Humans; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*