title: Cigarette smoking and colorectal cancer mortality among 602,242 Norwegian males and females.
abstract: BACKGROUND
  Colorectal cancer (CRC) is one of the main cancer types, with high incidence and mortality in Norway. We examined the association between different measures of smoking exposure and CRC mortality overall and by subsite in a large Norwegian cohort.
  
  
  METHODS
  We followed 602,242 participants from four Norwegian health surveys, aged 19-67 years at enrollment between 1972 and 2003 by linkage to the national registries through December 2007. We used Cox proportional hazard models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) by smoking categories for different CRC endpoints.
  
  
  RESULTS
  During a mean follow-up of 14 years, 2,333 Norwegian males and females died of CRC (60% men). Male and female ever smokers had a 20% (HR 1.23, CI 1.08-1.40 and HR 1.22, 95% CI 1.06-1.40, respectively) increased risk of death from CRC compared with sex-specific never smokers. For proximal colon cancer mortality, female ever smokers had a 50% (HR 1.49, 95% CI 1.20-1.87) increased risk compared with female never smokers. The increased risk of rectal cancer mortality was about 40% higher for male ever smokers (HR 1.43, 95% CI 1.14-1.81) compared with male never smokers. A test for heterogeneity by sex showed an increased risk of rectal cancer mortality among men which was significant for former smokers (Wald χ(2) =0.02) and an increased risk of proximal colon cancer mortality among women which was significant for ever and former smokers (Wald χ(2) =0.02 and χ(2) =0.04, respectively).
  
  
  CONCLUSIONS
  Smoking is associated with increased CRC mortality in both sexes. The risk of rectal and proximal colon cancer mortality was most pronounced among male and female smokers respectively.
authors.affiliation: Department of Community Medicine, Faculty of Health Sciences UiT, The Arctic University of Norway, Tromsø, Norway.
authors.forename: Ranjan
authors.initials: R
authors.lastname: Parajuli
authors.affiliation: Department of Community Medicine, Faculty of Health Sciences UiT, The Arctic University of Norway, Tromsø, Norway.
authors.forename: Eivind
authors.initials: E
authors.lastname: Bjerkaas
authors.affiliation: Division of Epidemiology, Department of Pharmacoepidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Aage
authors.initials: A
authors.lastname: Tverdal
authors.affiliation: Epidemiology Program, University of Hawaii Cancer Center, Honolulu, HI, USA.
authors.forename: Loïc
authors.initials: L
authors.lastname: Le Marchand
authors.affiliation: Department of Community Medicine, Faculty of Health Sciences UiT, The Arctic University of Norway, Tromsø, Norway ; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden ; Department of Genetic Epidemiology, Samfundet Folkhälsan, Helsinki, Finland ; Department of Research, Cancer Registry of Norway, Oslo, Norway.
authors.forename: Elisabete
authors.initials: E
authors.lastname: Weiderpass
authors.affiliation: Department of Community Medicine, Faculty of Health Sciences UiT, The Arctic University of Norway, Tromsø, Norway ; Norwegian Centre for Integrated Care and Telemedicine, University Hospital of North Norway, Tromsø, Norway.
authors.forename: Inger T
authors.initials: IT
authors.lastname: Gram
keywords: Norway; cigarette smoking; cohort study; colorectal cancer; mortality; sex
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