Abstract
BackgroundSmoking has recently been established as a risk factor for rectal cancer. We examined whether the smoking-related increase in rectal cancer differed by gender.MethodsWe 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.ResultsDuring 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).ConclusionsSmoking increases the risk of rectal cancer to the same extent in women as in men.
Highlights
Smoking has recently been established as a risk factor for rectal cancer
* Correspondence: inger.gram@uit.no †Equal contributors 1Department of Community Medicine, Faculty of Health Sciences, UiT, The Arctic University of Tromsø, Tromsø, Norway 7Norwegian Centre for Integrated Care and Telemedicine, University Hospital of North Norway, Tromsø, Norway Full list of author information is available at the end of the article we found that the increased risk of colon cancer due to cigarette smoking may be greater in women than men [2]
The Cox proportional hazards model was used with age as the underlying time scale to estimate multivariate-adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) for the associations between different measures of smoking exposure [age at smoking initiation in years (≤19, 20–24, ≥25), number of cigarettes smoked per day (1–9, 10–19, ≥20), smoking duration in years (1–19, 20–29, ≥30) and number of pack-years smoked (0–9, 10–19, ≥20)] and rectal cancer with never smokers as the reference group
Summary
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. An expert group at the International Agency for Research on Cancer (IARC) recently re-evaluated the carcinogenetic effects of smoking in humans, and concluded that smoking is a risk factor for both colon and rectal cancer [1]. In a recently published study based on present cohort, The variation in the smoking epidemic by country and gender was first described in a model focusing on the four stages of the tobacco epidemic in Western countries [3] and later in a more gender-specific model [4]. In Norway, the prevalence of daily smoking was around 25% for women and 65% for men in the 1950s. The prevalence of daily smoking has decreased steadily among men, while a decrease among women started only at the turn of the millennium. In 2007, about 24% of Norwegian men and women, aged 16 to 74 years were daily smokers [5,6]
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