Original articles—alimentary tract
Cigarette Smoking and the Risk of Colorectal Cancer: A Meta-analysis of Prospective Cohort Studies

https://doi.org/10.1016/j.cgh.2009.02.016Get rights and content

Background & Aims

Smoking has been implicated in many malignant diseases, but its association with colorectal cancer (CRC) is controversial. We quantitatively evaluated the relation between smoking and incidence of CRC in a meta-analysis of cohort studies.

Methods

Full publications of prospective cohort studies were identified in MEDLINE and EMBASE from 1950 to 2008. Subjects were classified as current smokers, former smokers, or never smokers. The quantity of smoking was assessed by number of cigarettes per day, years of smoking, and pack-years. The reported relative risks of CRC were pooled by random-effects model. Sensitivity analysis was conducted, and publication bias was evaluated.

Results

A total of 1,463,796 subjects were recruited in 28 prospective cohorts from America, Europe, and Asia, with median follow-up of 13 years (range, 4–30 years). Current smokers showed a modestly higher risk of CRC (relative risk [RR], 1.20; 95% confidence interval [CI], 1.10–1.30) than never smokers. The risk of CRC among male smokers (RR, 1.38; 95% CI, 1.22–1.56) was more significant than among female smokers (RR, 1.06; 95% CI, 0.95–1.19). Rectal cancer was more closely related to smoking (RR, 1.36; 95% CI, 1.15–1.61) than colonic cancer. Former smokers still carried a higher CRC risk than never smokers. The increased risk of CRC was related to cigarettes per day, longer years of smoking, or larger pack-years.

Conclusions

Smoking was associated with a significantly increased risk of CRC. The associated risk was higher for men and for rectal cancers. The association of tobacco consumption and CRC risk appeared to be dose-related.

Section snippets

Literature Search

All synonymous key words according to MeSH in study design, exposure, and outcome were used to identify the prospective cohort studies in MEDLINE from 1950 to April 2008 and EMBASE from 1980 to April 2008. Search terms included “prospective study,” “cohort study,” “colon/rectal/colorectal,” “cancer/neoplasm/carcinoma,” and “cigarette/tobacco/smoke.” Manual searches on the bibliographies of original articles or systematic reviews were also conducted. Only full publications from English-language

Results

We identified 2356 articles through searching in the database. All abstracts were scanned, and 132 full publications reporting cigarette smoking and CRC incidence were retrieved. Twenty-nine independent prospective cohort studies fulfilling inclusion criteria with report of CRC incidences were identified. We excluded 2 studies that reported only the risk of CRC among passive smokers46 or atomic bomb survivors from World War II.47 One study reported 2 separate groups of independent subjects

Discussion

Our meta-analysis of 28 prospective cohorts showed that smoking is associated with a modest but significantly increased risk of CRC, although no statistical significance was found among current female smokers, among men and women who smoked less than 20 cigarettes per day and smoked for less than 20 years, and also among those women who had less or even more than 20 pack-years. Compared with never smokers, current smokers who smoked at least 1 cigarette per day have an increase in the risk of

Acknowledgments

The authors thank Mr Andy Mak for his assistance in preparing this manuscript.

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    Conflicts of interest The authors disclose no conflicts.

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