In a multi-center study, patients who took one 80 mg aspirin a day — the same regimen recommended to reduce heart attack risk — reduced the risk of colon polyp recurrence by 19%, compared to patients given placebo (an inactive pill).

The study results were presented April 7 at the 93rd Annual Meeting of the American Association for Cancer Research.

An 80 mg aspirin is a standard baby aspirin. Patients who took adult aspirin (325 mg) also reduced the risk of adenoma, or polyp, recurrence, but only by 4%, said John A. Baron, MD, a professor of medicine at Dartmouth Medical School, Lebanon, N.H., and lead investigator for the study.

Polyps are pre-cancerous growths that are “very, very common among middle-aged people,” said Baron. "By age 50 or 60 about half the population has one or two polyps." When polyps are found during a colonoscopy, they are removed and examined to determine if they are benign or colon cancer.

Baron said the benefits of aspirin are more striking when only more aggressive polyps are analyzed. Daily baby aspirin dosing reduced the risk of recurrence of these growths by 40%, and regular dose aspirin reduced the risk by 19%.

In this study, researchers at nine North American centers enrolled 1,121 patients who had one or more polyps removed in the three months prior to study entry. Patients with known hereditary cancer syndromes were excluded.

“These were basically healthy patients in their 50s and 60s,” Baron said. For the first three months of the study all patients received 325 mg of aspirin daily. At three months, the patients were placed at random in three groups — getting a 325 mg dose, an 80 mg dose, or a placebo.

All patients were required to have follow-up colonoscopy at one to three years. The patients were followed for an average of 34 months and follow-up colonoscopy was completed in 97% of patients.

It is important to note that the study subjects were “supposed to have no remaining polyps in the large bowel after complete colonoscopy," Baron said. "But because we only did one colonoscopy it is very possible that one or two polyps were missed."

Patients had follow-up colonoscopy one to three years later and those “missed” polyps could have been detected in the follow-up colonoscopy. “So it could be that these data actually underestimate the benefit of aspirin,” said Baron.

While the results are encouraging, Baron said, it is “too soon to make a public health recommendation. I don’t think we can simply advise everyone to take aspirin to reduce the risk of colon cancer.”

Right now cardiologists recommend a daily baby aspirin to reduce the risk of heart attack in patients with heart disease, “so these results are good news for those patients because it is likely that the aspirin is also protecting their colons.”

Nonetheless, Baron warned, “aspirin is a real drug, with real side effects. It increases the risk of bleeding and of gastric complications. There is also a slight, but real, increased risk for stroke.”

So he urged patients to discuss the risks and benefits of daily aspirin therapy with their physicians before starting daily treatment. “And just because a single baby aspirin appears beneficial, that doesn't mean that four or five baby aspirin will increase the benefit,” he said.

AACR spokesman Allan H. Conney, PhD, director of the Laboratory for Cancer Research at Rutgers University, Piscataway, N.J., said several animal and observational studies have indicated, "that people who are ingesting aspirin chronically have a lower risk of colon cancer."

But Conney said the new study is particularly interesting for two reasons: a greater benefit for baby aspirin versus regular dose aspirin and the “greater effect of the aspirin on the more progressive, serious type of adenomas."

Baron said the study also investigated the use of folate treatment for prevention of recurrent polyps but that part of the study is not yet completed.