Randomized trials have considered short-term aspirin use for prevention of recurrent colorectal adenoma.
These trials have provided compelling evidence of a causal relationship between aspirin and colorectal neoplasia.
However, data on long-term risk of colorectal cancer according to dose, timing, or duration of therapy with aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) remain limited.
Dr Andrew Chan and colleagues from Massachusetts examined the influence of aspirin and NSAIDs in prevention of colorectal cancer.
The investigators conducted a prospective cohort study of 82,911 women enrolled in the Nurses' Health Study.
The Nurses' Health Study provided data on medication use biennially since 1980 and followed up through 2000.
|Significant risk reduction with aspirin was seen with more than 10 years of use|
|Journal of the American Medical Association|
The investigative team's main outcome measure was incident of colorectal cancer.
Over a 20-year period, the team documented 962 cases of colorectal cancer.
The investigators found that among women using aspirin of 2 x 325-mg tablets per week, the multivariate relative risk for colorectal cancer was 0.8.
However, the team did not observe significant risk reduction until more than 10 years of use.
The investigators noted that benefit appeared related to dose.
Compared with women who reported no use, the multivariate relative risks for cancer were 1.1 for women who used 0.5 to 1.5 standard aspirin tablets per week.
The team observed that relative risks for cancer for women using 2 to 5 aspirins per week was 0.9.
The relative risk for colorectal cancer in women was 0.8 with 6 to 14 aspirin per week, and 0.7 for more than 14 aspirin per week.
The team noted that women who used more than 14 aspirin per week for longer than 10 years in the past had a multivariate relative risk for cancer of 0.5.
A similar dose-response relationship was found for nonaspirin NSAIDs.
The investigators observed that the incidence of reported major gastrointestinal bleeding events per 1000 person-years also appeared to be dose-related.
The team found that among women who denied any aspirin use the relative risk was 0.8, and 1.1 for those using 0.5 to 1.5 standard aspirin tablets per week.
Relative risks for major gastrointestinal bleeding events were 1.1 for 2 to 5 aspirin/week, 1.4 for 6 to 14 aspirin/week; and 1.6 for more than 14 aspirin/week.
Dr Chan's team concluded, “Regular, long-term aspirin use reduces risk of colorectal cancer.”
“Nonaspirin NSAIDs appear to have a similar effect.”
“However, a significant benefit of aspirin is not apparent until more than a decade of use, with maximal risk reduction at doses greater than 14 tablets per week.”
“These results suggest that optimal chemoprevention for colorectal cancer requires long-term use of aspirin doses substantially higher than those recommended for prevention of cardiovascular disease, but the dose-related risk of gastrointestinal bleeding must also be considered.”