Purpose: Prior studies suggest cigarette smoking is associated with 1.5- to twofold increased risk of colorectal adenomas and possibly a higher risk of serrated polyps. Further clarification of risk differences between adenomas and serrated polyps is needed with regard to co-occurrence and polyp location.
Methods: We conducted a combined analysis of conventional adenoma and serrated polyp occurrence using individual-level data from 2,915 patients participating in three colonoscopy-based clinical trials. All participants had ≥1 adenomas removed at baseline and were followed for up to 4 years. Smoking habits and other lifestyle factors were collected at baseline using questionnaires. We used generalized linear regression to estimate risk ratios and 95 % confidence intervals.
Results: Smokers were at slightly increased risk of adenomas compared to never smokers [current: RR 1.29 (95 % CI 1.11-1.49) and former: RR 1.18 (1.05-1.32)]. Smoking was associated with greater risk of serrated polyps [current: RR 2.01 (1.66-2.44); former: RR 1.42 (1.20-1.68)], particularly in the left colorectum. Associations between current smoking and occurrence of serrated polyps only [RR 2.33 (1.76-3.07)] and both adenomas and serrated polyps [RR 2.27 (1.68-3.06)] were more pronounced than for adenomas only [RR 1.31 (1.08-1.58)]. Results were similar for other smoking variables and did not differ by gender or for advanced adenomas.
Conclusions: Cigarette smoking has only a weak association with adenomas, but is associated with a significantly increased risk of serrated polyps, particularly in the left colorectum. Since a minority of left-sided serrated polyps is thought to have malignant potential, the role of smoking in initiation phases of carcinogenesis is uncertain.