Abstract & Commentary
Synopsis: Although regular aspirin use reduces the risk for colorectal adenoma formation as shown in previous randomized-controlled trials, the protective effect now seems to be greatest at substantially higher doses (> 14 standard tablets/week) than currently recommended for cardiovascular prophylaxis.
Source: Andrew T, et al. Ann Intern Med. 2004;140:157-166.
In the context of the Nurses’ Health Study of 27,007 women, 1368 cases of colorectal adenoma were diagnosed between 1980 and 1998. Risks for adenoma were lower for all users taking 2 standard aspirin tablets per week, but protection against adenomas was quite clearly dose—but not duration—related. The maximum effect on development of distal colonic neoplasia was associated with more than 14 standard aspirin tablets daily. These aspirin effects on colon neoplasia were not modified by age, postmenopausal hormone use, or family history of colorectal cancer.
Concomitant NSAID use didn’t affect these results one way or the other. Other studies cited by Andrew and colleagues also support a dose-effect for aspirin in the prevention of colorectal neoplasia. However, up to 1% of chronic aspirin users of higher than cardiovascular prophylactic doses will have GI bleeding, and intracerebral bleeding may also occur in a dose-related pattern with aspirin administration. The divergence of the aspirin dose for safe cardiovascular prophylaxis and the dose that may be required for colorectal adenoma prevention may preclude the consideration of aspirin for the latter indication.
Comment by Malcolm Robinson, MD, FACP, FACG
The study has some defects. First, we really don’t know the exact doses of aspirin used by study participants since aspirin was self-administered and only later self-reported by the nurses studied. Only distal colon adenomas were considered since many patients did not have complete colonoscopic surveillance. Still, this is a very carefully done study in a large population. An editorial accompanying this article by the epidemiologist Robert Sandler points out that the risks associated with aspirin almost certainly outweigh its benefits as potentially widely used prophylaxis against colonic neoplasia.1 Still, those individuals who are using low-dose aspirin for cardiovascular prophylaxis can enjoy the additional satisfaction that this same medicine may also be providing at least slight protection against the development of colorectal adenomas.
Dr. Robinson, Medical Director, Oklahoma Foundation for Digestive Research; Clinical Professor of Medicine, University of Oklahoma College of Medicine, Oklahoma City, OK, is Associate Editor of Internal Medicine Alert.
1. Sandler RS. Ann Intern Med. 2004;140:224-225.