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To the Editor: In their study on aspirin, nonsteroidal anti-inflammatory drugs, and the risk of colorectal cancer, Dr Chan and colleagues¹ conclude that regular, long-term aspirin use reduces risk of colorectal cancer. Although the study shows that long-term users of aspirin have a lower incidence of colorectal cancer, aspirin itself may not be the cause of this observation. The situation may be analogous to earlier results of the Nurses' Health Study,² in which the apparent reduced cardiac and mortality risks from estrogen use may have been artifacts of confounding or selection bias, based on results of a subsequent randomized controlled trial.³

In the study by Chan et al, there was a greater percentage of nonwhite participants among the aspirin nonusers compared with the users, an important difference. It is not clear if the relative risks were adjusted for race, but when there are measured confounders there also are likely to . . . [Full Text of this Article]

Gregory C. Vachon, MD
gvachon1@ccbhs.org
Austin Health Center
Ambulatory and Community Health Network
Cook County Bureau of Health Services
Chicago, Ill

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