The authors caution that the results for continuous, long-term low-dose aspirin should be interpreted with caution, as these individuals comprised only a small subgroup (2-3% of all low-dose aspirin users) of the study population, and these persons may have a risk profile for colorectal cancer that differs from that of the general population. There was no association between ever use of low-dose aspirin and colorectal cancer risk and no substantial variation between recent and former use. The results indicate that if aspirin is taken at doses of 75-150 mg, long-term, continuous use is necessary to achieve a substantial protective effect against colorectal cancer.
The authors go on to discuss the current literature on aspirin and colorectal cancer prevention, noting that the evidence is inconclusive despite a large body of research. Some studies have suggested any protective effect of aspirin may be largely confined to tumours in the proximal colon but results are inconsistent.
The results for non-aspirin NSAIDs are similar to those of other studies; concerns about gastrointestinal and cardiovascular safety do however limit any potential for these agents in cancer prevention.
The study had a number of limitations, including lack of data on use of over the counter NSAIDs, possible exposure misclassification, and the possibility of residual confounding introduced by unmeasured factors (e.g. physical activity; diet; obesity; family history of colorectal cancer).