Cigarette smoking and risk of colorectal cancer among Norwegian women.
OBJECTIVE
The association between cigarette smoking and colorectal cancer (CRC) is still not established. In 2002, Norwegian women had the second highest incidence of CRC in the world. A large proportion of Norwegian women are ever smokers. We examined the association between cigarette smoking and CRC incidence among Norwegian women.


METHODS
We followed 68,160 women, aged 30-69 years, from the Norwegian Women and Cancer Study who completed a questionnaire in 1996 or 1998 by linkages to national registers through 31 December 2005. Rate ratios (RRs) and 95% confidence intervals (CIs) were estimated by fitting Cox proportional hazard models. Subsequently, we estimated the population attributable fraction.


RESULTS
Altogether, 425 incident cases of primary, invasive CRC were identified. Ever smokers had a 20% increased risk of CRC (RR = 1.2; 95% CI = 1.0-1.5), a 30% increased risk of colon (RR = 1.3; 95% CI = 1.0-1.7), and a 10% increased risk of rectal (RR = 1.1; 95% CI = 0.7-1.5) cancer compared to never smokers. The population attributable fraction was estimated to be 12% which indicated that approximately one in eight of the CRC cases could have been prevented at a population level.


CONCLUSIONS
Our results support the hypothesis that cigarette smoking is a preventable cause of CRC among women.
Gram
Inger T
IT
Institute of Community Medicine, University of Tromsø, Breivika, Tromsø N-9037 Norway. inger.gram@ism.uit.no
Braaten
Tonje
T
Lund
Eiliv
E
Le Marchand
Loic
L
Weiderpass
Elisabete
E
D000328:Adult; D000368:Aged; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000209:etiology* / Q000473:pathology* / Q000517:prevention & control; D016001:Confidence Intervals; D003625:Data Collection; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009361:Neoplasm Invasiveness / Q000473:pathology; D009664:Norway / Q000453:epidemiology; D011159:Population Surveillance; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D011795:Surveys and Questionnaires