Chan AT et al. (2005) Long-term use of aspirin and nonsteroidal anti-inflammatory drugs and risk of colorectal cancer. JAMA 294: 914–923

A prospective cohort study involving 82,911 female participants has shown that regular long-term use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) reduces the risk of colorectal cancer.

The study population was recruited from the Nurses' Health Study, a study established in 1976 that enrolled US female registered nurses. Every 2 years, questionnaires were sent to the participants asking about their medicine use, including that of aspirin and other NSAIDs. Information specifically about cyclo-oxygenase 2 inhibitors was not collected.

Colorectal cancer was documented in 962 of the participants. Long-term regular aspirin use (2 or more standard tablets per week) was associated with a significant reduction in risk of colorectal cancer. The apparent benefit associated with aspirin use was substantially greater with increasing aspirin dose, and the greatest risk reduction was observed in women taking more than 14 doses of aspirin per week. Increased duration of aspirin use was also associated with progressively reduced risk of colorectal cancer, although significant benefit was not evident until more than 10 years' usage. The results for non-aspirin NSAIDs were comparable with those for aspirin. As well as the apparent benefit of aspirin and NSAIDs, increased dosages were associated with increased gastrointestinal bleeding.

The investigators note that further studies to address the risk–benefit profile of long-term aspirin or NSAID use in various risk groups, compared with other potential cancer prevention strategies, are warranted.