Cigarette smoking does appear to be linked to a higher risk of colorectal adenoma, to a large enough degree that perhaps smoking history should be considered in guidelines for colonoscopy screening, Edoardo Botteri and colleagues reported.
The smoking-associated risk described in the report, a meta-analysis of 42 studies, indicates that a person who has smoked two packs per day for 25 years has almost twice the risk (relative risk, 1.88) of having a colorectal adenoma as a person who has never smoked, reported Mr. Botteri of the division of epidemiology and biostatistics at the European Institute of Oncology, Milan, and his colleagues.
The meta-analysis also indicated that the association between smoking and adenomatous polyps was stronger for high-risk adenomas than for low-risk adenomas. That finding contradicts some previous observations, made based on single studies, and suggests that smoking probably is associated with a higher risk of colon cancer. In the past, this question has been unresolved, the authors said (Gastroenterology 2008;134:388-95).
The investigators began by conducting a search of the PubMed database for relevant studies, and then scanned the references of the studies they reviewed to identify any studies they might have missed.
In total they identified 125 studies worthy of review, of which 42 were either independent case-control or nested case-control studies that met the criteria for inclusion in the meta-analysis. Twenty-six of those studies used colonoscopy or sigmoidoscopy plus barium enema and x-ray to view the entire colon. Sixteen studies used only sigmoidoscopy and did not view the entire colon.
After they pooled the data from the studies, the investigators found that current smokers had a relative risk for colorectal adenoma of 2.14, compared with never smokers. The pooled estimate for former smokers versus never smokers was a relative risk of 1.47, and the pooled estimate for ever smokers versus never smokers was a relative risk of 1.82.
When the investigators analyzed the data from a dose-response point of view, assuming a linear increase in risk, they found a 13% increased risk of presenting with adenomatous polyps for every additional 10 pack-years smoked, relative to never smokers. …