The Pharmaceutical Journal
Vol 270 No 7240 p358
15 March 2003

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The New England Journal of Medicine abstracts (one) and (two)

Aspirin prevents colon adenomas

Two recent studies, published in The New England Journal of Medicine show that aspirin prevents colorectal adenoma, the precursor to most colorectal cancers (2003;348:883 and 891).

In the first, Dr Robert Sandler, of the University of North Carolina, Chapel Hill, and colleagues treated 635 patients with prior colorectal cancer with aspirin 325mg daily or placebo for a median 12.8 months.

One or more adenomas were detected by colonoscopy in 17 per cent of patients in the aspirin group and 27 per cent of patients in the placebo group, giving an adjusted relative risk of 0.65 for recurrent adenoma in the aspirin group.

The mean number of adenomas was lower in the patients treated with aspirin. Also, the median time to detection of a first adenoma was 15.5 months in the aspirin group compared with 11.3 months in the placebo group. In contrast, aspirin had no effect on the size of the largest adenoma or the number of patients with advanced tumours. This led the researchers to conclude: "Daily use of aspirin is associated with a significant reduction in the incidence of colorectal adenomas in patients with previous colorectal cancer."

Similar findings were forthcoming from the other study led by Dr John Baron, of the Dartmouth–Hitchcock Medical Center, Lebanon, New Hampshire. They treated 1,121 patients with a recent history of colorectal adenoma with aspirin 81mg or 325mg daily for at least a year. Colonoscopy revealed that incidence of adenoma and relative risk were lower in the group receiving 81mg aspirin than in the higher dose and placebo groups.

Dr Sandler and his colleagues suggest that the apparently better result with low-dose aspirin may be due to the fact that they used higher risk patients who would require a greater dose of aspirin than those in Dr Baron's study. The difference could also be merely down to chance.

In an accompanying article, Dr Thomas Imperiale, Indiana University school of medicine, states that a protective effect of aspirin is biologically plausible because it inhibits cyclo-oxygenase-2, an enzyme found in colorectal cancer tissue, and epidemiological studies have consistently shown a 40–50 per cent reduction in colorectal cancer risk (ibid, p879). He points out that aspirin appears to have greater efficacy than previously reported dietary or nutritional interventions for preventing colorectal adenoma. In contrast, Dr Imperiale draws attention to the fact that there was no reduction in cancer incidence in the only randomised trial of aspirin conducted to date.

The conclusions of Dr Sandler and colleagues are cautious: "Adenomas developed in some patients in the aspirin group. For that reason, aspirin cannot be viewed as a replacement for surveillance colonoscopy. Before aspirin use can be recommended for patients with colorectal cancer, the risks and benefits will need to be compared with those of alternative chemopreventive agents."