A daily aspirin dose can sharply reduce the risk of colorectal cancer in people who are at high risk of developing the disease, according to two new studies released today.
The findings add to the mounting evidence that aspirin protects against this deadly disorder, but scientists are not yet ready to recommend everyone start taking it routinely because it is still unclear whether the benefits outweigh the risks.
The simple drug may yet prove to be a wonder drug because of its beneficial effects on inflammation, heart disease and, now, the gastrointestinal system, but it can be a double-edged sword whose long-term use is associated with intestinal bleeding, ulcers and stroke.
"Aspirin may be of some benefit in preventing colorectal cancer," said Dr. Thomas Imperiale of the Indiana University School of Medicine. But, he added, colonoscopy and other forms of surveillance are much more effective in reducing the risk of developing the disease.
When men and women are considered together, colorectal cancer is the second most deadly form of cancer, after lung cancer. The American Cancer Society said about 147,500 Americans are expected to develop the disease this year and 57,100 are expected to die from it.
Early signs of the disease can be detected by fecal blood tests. Doctors now recommend that everyone undergo colonoscopy at age 50 and then every two to three years after that if intestinal growths, known as polyps, are detected and removed. If no polyps are present, the test should be repeated every 10 years. Many people do not receive the test, however, because of the cost and the inconvenience.
Aspirin has previously been shown to have powerful benefits in reducing the risk of heart attack, but even with that condition physicians recommend it only for those with the highest risk of developing cardiovascular disease, because of the long-term risks.
Its usefulness in colorectal cancer has previously been shown in epidemiological studies conducted primarily among people with arthritis, who routinely take large doses of aspirin to ease symptoms. Various studies have shown that aspirin use reduces colorectal cancer in this group by about a third to a half.
In another epidemiological study released Tuesday, Italian researchers reported that aspirin consumption also reduces the risk of developing cancers of the throat, mouth and esophagus, suggesting that it may protect the entire alimentary canal.
But proof generally requires clinical trials, and today's reports mark the first of those. Both studies were sponsored by the National Institutes of Health through a group of researchers called the Cancer and Leukemia Group B. Both studies focused on polyps, which are generally considered precursors of tumors, because they develop much faster, allowing completion of the studies in a reasonable amount of time.
The first study enrolled 517 people who previously had a colorectal tumor successfully removed by surgery. Half received a daily 325-milligram coated aspirin tablet and half a placebo.
The team reports in today's New England Journal of Medicine that, after three years, only 17% of those taking aspirin had developed polyps, compared with 27% of those receiving the placebo -- a reduction of more than a third. Among those taking aspirin who did develop polyps, moreover, the number of polyps was lower, and they developed more slowly.
The results were so successful that the study was halted prematurely so that all participants could begin taking aspirin.
Taking aspirin "provides a new way to lower the risk of recurrence in patients who have had colon cancer," said Dr. Richard Schilsky of the University of Chicago, chairman of the group.
The second study involved 1,121 people who had previously had polyps surgically removed, but who never had cancer. The subjects received either a regular, 325-milligram aspirin daily, an 81-milligram aspirin (baby aspirin) or a placebo. All of the patients were monitored for at least a year. The results proved somewhat more complicated.
Among those receiving a placebo, 47% developed one or more polyps during the study. Among those receiving regular aspirin daily, 45% developed polyps. But among those receiving the baby aspirin, 38% developed polyps.
"The difference between the two studies could be that we enrolled higher-risk patients, or it could simply be due to chance," the group wrote in the second article.
The results appear straightforward, but Imperiale cautioned that side effects cloud the issue. He calculated that 471 people would have to take aspirin for at least five years to prevent one case of colorectal cancer, and 1,250 people would have to take it for at least 10 years to prevent one death.
And for every person who is spared from colorectal cancer, there would be one person who suffered from major bleeding as a result of the aspirin therapy. Furthermore, he said, more people would suffer strokes caused by the aspirin than would be spared death from cancer.
The bottom line, said Dr. Robert Halle of USC's Keck School of Medicine, who participated in the study, is that "patients should discuss this with their doctor to see if it makes sense for them."