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BACKGROUND:Aspirin for prevention of colorectal cancer is controversial. PURPOSE: Toexamine the benefits and harms of aspirin chemoprevention. DATA SOURCES:MEDLINE, 1966 to December 2006; EMBASE, 1980 to April 2005; CENTRAL, CochraneCollaboration's registry of clinical trials; Cochrane Database of SystematicReviews. STUDY SELECTION: Two independent reviewers conducted multilevelscreening to identify randomized, controlled trials (RCTs), case-controlstudies, and cohort studies of aspirin chemoprophylaxis. For harms, systematicreviews were sought. DATA EXTRACTION: In duplicate, data were abstracted andchecked and quality was assessed. DATA SYNTHESIS: Regular use of aspirinreduced the incidence of colonic adenomas in RCTs (relative risk [RR], 0.82[95% CI, 0.7 to 0.95]), case-control studies (RR, 0.87 [CI, 0.77 to 0.98]), andcohort studies (RR, 0.72 [CI, 0.61 to 0.85]). In cohort studies, regular use ofaspirin was associated with RR reductions of 22% for incidence of colorectalcancer. Two RCTs of low-dose aspirin failed to show a protective effect. Datafor colorectal cancer mortality were limited. Benefits from chemopreventionwere more evident when aspirin was used at a high dose and for periods longerthan 10 years. Aspirin use was associated with a dose-related increase inincidence of gastrointestinal complications. LIMITATIONS: Important clinicaland methodological heterogeneity in the definitions of regular use, dose, andduration of use of aspirin necessitated careful grouping for analysis.CONCLUSIONS: Aspirin appears to be effective at reducing the incidence ofcolonic adenoma and colorectal cancer, especially if used in high doses formore than 10 years. However, the possible harms of such a practice requirecareful consideration. Further evaluation of the cost-effectiveness ofchemoprevention compared with, and in combination with, a screening strategy isrequired. Leggil'articolo