[Aspirin in the prevention of colorectal cancer]

Colorectal adenomas are precursors of most colorectal cancers and are consequently a surrogate endpoint for assessing the efficacy of chemopreventive agents. Cyclooxygenase-2 (COX-2) levels have been found to be increased in a significant number of colorectal carcinomas and adenomas. COX-2 overexpression is linked to carcinogenesis due to increased production of prostaglandins, which seem to play an important role in angiogenesis, cell proliferation and migration, as well as in apoptosis. These data support the use of acetylsalicylic acid (AAS) or aspirin, a COX-2 inhibitor, as an effective agent in colorectal cancer prevention. Several cohort and case control studies have shown that regular use of aspirin reduces the risk of colorectal cancer by approximately 50%. However, randomized controlled trials of aspirin report discrepant results, although there is an decrease in the relative risk of adenoma recurrence of approximately 17%. To date, although there is compelling evidence that the use of aspirin protects against adenoma and colorectal cancer, the optimal dose and duration of aspirin required to obtain this effect remain to be defined. Probably, the longer the treatment duration--even for more than 10 years--and possibly with higher doses, the greater the protective effects of aspirin. Finally, these benefits need to be considered in the context of all of the health effects of prolonged aspirin use, both positive and negative.