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Cigarette smoking is associated with increased risk for colorectal cancer (CRC), but the strength of the association, whether a dose-response exists, the effect of quitting, and the effect of smoking on different CRC subtypes are uncertain. To summarize the available evidence on these issues, investigators conducted a meta-analysis of 188 studies. Results include the following:
Compared with never-smokers, the relative risks (RRs) for CRC were 1.14 for current smokers (88 studies), 1.17 for former smokers (79 studies), and 1.18 for ever-smokers (131 studies). The corresponding RRs for colon cancer were 1.05, 1.15, and 1.11, respectively, and those for rectal cancer were 1.16, 1.17, and 1.15, respectively.
A dose-response effect was observed f…