Open Access Highly Accessed Research article

Smoking increases rectal cancer risk to the same extent in women as in men: results from a Norwegian cohort study

Ranjan Parajuli1, Eivind Bjerkaas1, Aage Tverdal2, Loïc Le Marchand3, Elisabete Weiderpass1456 and Inger T Gram17*

Author Affiliations

1 Department of Community Medicine, Faculty of Health Sciences, UiT, The Arctic University of Tromsø, Tromsø, Norway

2 Division of Epidemiology, Department of Pharmacoepidemiology, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, 0403 Oslo, Norway

3 Epidemiology Program, University of Hawaii Cancer Center, Honolulu, HI, USA

4 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

5 Department of Genetic Epidemiology, Samfundet Folkhälsan, Helsinki, Finland

6 Department of Research, Cancer Registry of Norway, Oslo, Norway

7 Norwegian Centre for Integrated Care and Telemedicine, University Hospital of North Norway, Tromsø, Norway

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BMC Cancer 2014, 14:321  doi:10.1186/1471-2407-14-321

Published: 6 May 2014



Smoking has recently been established as a risk factor for rectal cancer. We examined whether the smoking-related increase in rectal cancer differed by gender.


We followed 602,242 participants (49% men), aged 19 to 67 years at enrollment from four Norwegian health surveys carried out between 1972 and 2003, by linkage to Norwegian national registries through December 2007. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated by fitting Cox proportional hazard models and adjusting for relevant confounders. Heterogeneity by gender in the effect of smoking and risk of rectal cancer was tested with Wald χ2.


During a mean follow-up of 14 years, 1,336 men and 840 women developed invasive rectal cancer. Ever smokers had a significantly increased risk of rectal cancer of more than 25% for both men (HR = 1.27, 95% CI = 1.11-1.45) and women (HR = 1.28, 95% CI = 1.11-1.48) compared with gender-specific never smokers. Men smoking ≥20 pack-years had a significantly increased risk of rectal cancer of 35% (HR = 1.35, 95% CI = 1.14-1.58), whereas for women, it was 47% (HR = 1.47, 95% CI = 1.13-1.91) compared with gender-specific never smokers. For both men and women, we observed significant dose–response associations between the risk of rectal cancer for four variables [Age at smoking initiation in years (both ptrend <0.05), number of cigarettes smoked per day (both ptrend <0.0001), smoking duration in years (ptrend <0.05, <0.0001) and number of pack-years smoked (both ptrend <0.0001)]. The test for heterogeneity by gender was not significant between smoking status and the risk of rectal cancer (Wald χ2, p -value; current smokers = 0.85; former smokers = 0.87; ever smokers = 1.00).


Smoking increases the risk of rectal cancer to the same extent in women as in men.

CONOR; Cigarette smoking; Rectal cancer; Cohort; Norway