Aspirin for the Prevention of Colorectal Cancer
Two recent studies in the New England Journal of Medicine suggest daily aspirin use can help prevent the growth of adenomatous polyps in the large intestine. These mushroom-shaped growths may slowly develop into colon cancer, the second leading cause of cancer deaths in the U.S.
One study investigated the effect of aspirin on the incidence of polyps in over 500 patients with a history of colon cancer. The participants were randomly assigned to receive a daily 325-mg dose of aspirin or a placebo. The patients underwent colonoscopies to detect growths. After an average of 2½ years, only 17% percent of the patients who received aspirin had developed at least one polyp, compared to 27% of the patients who received the placebo. And of those who did have growths, patients in the aspirin group had fewer polyps than patients in the placebo group. Aspirin also appeared to delay the development of polyps. However, the average size of the growths and the proportion of patients with advanced (larger, more abnormal, or cancerous) polyps did not differ between the two groups.
In a similar study, over 1,100 patients with a history of polyps were randomly assigned to receive either a placebo, 81 mg of aspirin, or 325 mg of aspirin. After an average of 33 months, patients who received 81 mg of aspirin had a 19% lower risk of developing a polyp than patients in the placebo group. Patients who received 325 mg of aspirin did not have a significantly lower risk of developing polyps than the patients who received the placebo. This finding was somewhat unexpected and the researchers believe it may be the result of chance. In contrast to the study mentioned above, this one found patients in the low-dose group had a more than 40% lower risk of developing advanced polyps than the placebo group.
Despite the results of these studies, experts are stopping short of recommending daily use of aspirin to prevent colon cancer. While aspirin can help thwart the formation of polyps, only a small number of polyps actually develop into cancerous tumors. And from the mixed results of the two studies it's not clear that aspirin keeps those few polyps from becoming advanced. Certainly screening for colon cancer is still necessary. While longer studies are needed to clarify aspirin's benefit and the proper dose, at this point screening through colonoscopies and other detection methods saves more lives. In addition, the risk of intestinal bleeding associated with prolonged use of aspirin can't be ignored.
So for now, don't take a daily dose of aspirin for the prevention of colon cancer, unless your doctor recommends it. Also, if you have a history of polyps or colon cancer, talk with your doctor about prevention strategies. And remember to be screened regularly!
April 2003 Update