March 5, 2003 -- People who take aspirin to protect their hearts may also be protecting themselves against one of the leading causes of cancer death. Two new studies suggest that an aspirin a day may help prevent the formation of polyps that can lead to colon cancer.
Researchers found that a daily aspirin significantly reduced the recurrence of colon polyps among people with previous colon cancers. A weaker association was seen for patients with a history of polyps but no cancer. But it is too soon to recommend that anyone -- even those at high risk -- take aspirin or any other anti-inflammatory drug solely to lower their colon cancer risk, the researchers say.
The studies appear in the March 6 issue of The New England Journal of Medicine.
"Screening is still the most important thing that people can do to protect themselves against colorectal cancer," lead researcher Robert S. Sandler, MD, tells WebMD. "The worst thing that could happen is for people to get the idea that they don't have to get screened if they take aspirin. But these studies do suggest that aspirin helps prevent the development of colon polyps."
Each year, roughly 57,000 Americans die of colon cancer, making it the second leading cause of cancer deaths overall. The risk of developing colon cancer and the polyps that can lead to the disease increases with age. Nine out of 10 people diagnosed with colon cancer are over the age of 50.
Previous trials attempting to show a protective benefit for dietary fiber, antioxidant vitamins, and diet have proved disappointing. There is some evidence that dietary calcium protects against the formation of polyps, but the findings are not conclusive.
Animal trials and preliminary studies in humans have suggested that regular aspirin use lowers the risk of colon cancer. To further test this theory, Sandler and colleagues recruited more than 1,100 patients with a history of polyps and 635 patients with a history of colon cancer.
The colon cancer patients were treated with a regular, coated aspirin (325 mg) or placebo daily. The trial was stopped early, after roughly 31 months, because the aspirin group had significantly fewer polyps.
The study group with a history of polyps but not cancer received daily doses of low-dose aspirin (81 mg), a regular aspirin, or placebo for an average of just under three years. The patients in the two aspirin groups had a lower rate of polyp recurrence than those in the placebo group. But, inexplicably, the patients given low-dose aspirin had better responses than patients taking the higher dose of aspirin every day.
Although other nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, were not tested, there is good reason to believe that they also help prevent precancerous polyps from forming. A large study is now under way assessing whether one of the newest class of NSAIDs, Cox-2 inhibitors, helps prevent colon cancer. Cox-2 inhibitors include Bextra, Celebrex, and Vioxx. The hope is that these drugs will work as well or better than aspirin but with fewer side effects. Regular use of aspirin and many other NSAIDs is associated with an increased risk for stomach or intestinal bleeding.
In an editorial accompanying the two studies, Indiana University School of Medicine Professor Thomas F. Imperiale, MD, writes that it is unlikely there will be a definitive clinical trial of aspirin or other NSAIDs for the prevention of colon cancer. He agrees that although aspirin and other NSAIDs may have a modest impact on colon cancer risk, the evidence is not strong enough to recommend their routine use for preventing the cancer.
"The bottom line is that these trials are a step in the right direction, but we have not reached the threshold where we can change clinical practice," he tells WebMD. "This suggests that people already on aspirin therapy may derive an additional benefit. But the best prevention for colorectal cancer is still regular screening once you hit the age of 50."