WEDNESDAY, March 5, 2003 (HealthDayNews) -- People who have had colorectal cancer or a history of intestinal polyps can reduce the incidence of those polyps by taking an aspirin a day, two studies show.
However, that doesn't mean everyone should start popping aspirin to prevent cancer, experts say.
"These studies don't say anything about a normal person who does not have a history of colorectal cancer," says Electra Paskett, associate director of population sciences at Ohio State University and chair of the committee that oversaw one of the studies. "The best thing most people can do is get the appropriate screening for colorectal cancer."
Trials to see whether the prescription nonsteroidal anti-inflammatory drugs (NSAIDs) that work in the same way as aspirin for the general population are under way, but results are not expected until next year at the earliest.
The study in which Paskett participated was done at three dozen cancer centers, which enlisted 635 patients with a history of colon cancer. Half took a daily aspirin tablet of standard adult size, 325 milligrams, while the other half took a placebo.
After a year, 17 percent of people in the aspirin group had developed polyps, compared to 27 percent of those in the placebo group, says a report in the March 6 issue of The New England Journal of Medicine. There was no difference in the size of the polyps or of adverse effects, the report says.
The second study, led by doctors at the Dartmouth-Hitchcock Medical Center, included 1,024 people with a history of intestinal polyps. It produced one puzzling result: the incidence of polyps in those who took a smaller daily dose of aspirin, 81 milligrams, was 38 percent, lower than the 45 percent incidence of those who took 325 milligrams daily. However, the incidence in people who took a placebo was highest, at 47 percent.
"I just don't understand why that happened," Paskett says.
It's not exactly clear why aspirin prevents formation of intestinal polyps, says Dr. Thomas F. Imperiale, professor of medicine at the University of Indiana School of Medicine and author of an accompanying editorial. But both aspirin and more expensive NSAIDs such as Celebrex and Vioxx work in the same way, by inhibiting the action of an enzyme called cox-2, Imperiale says, and high levels of that enzyme are found in colon cancers. Cox-2 is believed to help increase cancerous cell growth and invasion, he says.
The newly reported studies are just one step in clarifying the role of NSAIDs in colorectal cancer. "There is not a lesson in them" for the general population, he says. "This is a proof-of-principle pair of trials. They say that aspirin can reduce the risk of recurrent polyps, but they don't say anything else."
Most of all, Imperiale says, the studies "do not say that people should take aspirin instead of the recommended steps for prevention of colorectal cancer."
The real importance of the study is scientific, says Dr. Robert Greenberg, professor of medicine at Dartmouth: "It gives us a better understanding of the factors that might be involved in causing cancer."
As for the population at large, "if someone is considering taking aspirin to prevent heart disease, this might be one piece of information that pushes him off the fence," Greenberg says.
The American Cancer Society estimates that more than 147,000 cases of colorectal cancer will be diagnosed this year in the United States, and that it will cause more than 57,000 deaths. The society recommends yearly stool examinations and digital rectal examinations for persons over 40, sigmoidoscopy at age 50 and every three to five years after that, and colonoscopy at age 35 to 40 for those with a close relative diagnosed with the cancer at an early age.
More information
You can learn more about measures to prevent colorectal cancer from Memorial Sloan-Kettering Cancer Center or the National Cancer Institute.
