Colorectal cancer is the third most common cancer in the U.S. According to the American Cancer Society, an estimated 147,500 new cases of colorectal cancer will be diagnosed, and approximately 57,000 people will die of the disease this year. Previous research in this area has suggested that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) may reduce the incidence of colorectal adenomas (a type of pre-cancerous polyps) and colorectal cancer deaths.

Now, two clinical trials published in the March 6, 2003 issue of the New England Journal of Medicine add to the growing list of potential benefits of aspirin—that widely available and inexpensive drug—in the prevention of chronic disease.

About the studies

In the first study, researchers attempted to determine whether or not aspirin reduced the risk of developing colorectal adenomas. In this study, 1121 subjects recently diagnosed with one or more adenomas were randomly assigned to receive daily doses of either placebo, 81 mg of aspirin (baby-aspirin dose), or 325 mg of aspirin (adult dose). Researchers were primarily interested in determining the percentage of patients who developed one or more adenomas after at least one year of therapy.

In the second study, researchers wanted to know what effect aspirin would have on the incidence of colorectal adenomas in subjects with a history of colorectal cancer. In this study, 635 subjects were randomized to receive either 325 mg of coated aspirin per day or placebo. This time, the researchers were interested in three things: the proportion of subjects who developed adenomas, the number of adenomas detected, and the length of time required for the adenoma to develop.

The findings

The researchers in the first study found that 47% of the subjects in the placebo group, 38% in the baby aspirin group, and 45% in the adult aspirin group, developed one or more adenomas after at least one year. This translated into a statistically significant 19% overall reduction in risk of polyp recurrence in the baby aspirin group. Curiously, there was no significant risk reduction in the adult aspirin group compared to the placebo group. Even more significantly, the researchers found that the risk of advanced disease (larger, more serious adenomas or invasive cancer) was 41% lower in the baby aspirin group alone. Again, the adult dose showed a lesser preventive effect, which was not statistically significant.

In the second study, the researchers found that only 17% of subjects in the aspirin group developed adenomas as compared to 27% in the placebo group, a statistically significant difference. The researchers also found that subjects in the aspirin group who did develop adenomas averaged fewer than those in the placebo group, and that the adenomas in the aspirin group took longer to develop. This study was stopped early because the effect of the aspirin was so significant.

How does this affect you?

Researchers from the first study say it is not clear why the 81 mg dose of aspirin appeared to be more effective than the 325 mg dose, but suggest the possibility that only a low dose is required for a preventive effect. It was also not clear why the 325 mg dose produced different results in the first study than in the second. Researchers believe it may reflect the fact that the patients in the second study were at a significantly higher risk of developing colorectal cancer, because they had been treated for the disease previously.

Despite these differences, researchers say that both studies support the use of aspirin as a means of reducing the rate of adenoma recurrence. This means that, in addition to its favorable affect on cardiovascular disease risk, an aspirin a day appears to reduce the risk of colorectal cancer.

Despite these positive results, researchers don’t recommend taking an aspirin a day until you have discussed it with your doctor. Even low-dose aspirin can have adverse effects in some patients. They also warn that although the studies results are very positive, for patients who have a history of colorectal cancer, regular colonoscopy and polyp removal are still the most effective method of preventing recurrence.