Aspirin may block colon cancer, studies show

Drug is modestly effective in preventing polyps

March 06, 2003|By Jonathan Bor | Jonathan Bor,SUN STAFF

A daily dose of aspirin, the aches-and-pains remedy that prevents recurrent heart attacks and certain kinds of strokes, has also shown promise in preventing cancer.

Two studies appearing today in a major medical journal found that aspirin is modestly effective in preventing recurrences of the benign growths, or polyps, that trigger colon cancer.

But researchers involved in the studies cautioned yesterday that it is too soon to make a blanket recommendation that people take aspirin to ward off colon cancer, the second-leading cause of cancer deaths in the United States.

So far, they cautioned, the benefits don't appear to outweigh the risks of complications, such as stomach ulcers and kidney problems. But some people at high risk for the disease might want to ask their doctors whether it is appropriate for them, researchers said.

"While we celebrate the modest effect aspirin had in this very defined group of people, it's too early to recommend that an aspirin a day can keep cancer away," said Dr. Richard Rothstein, a Dartmouth University physician and author of one of the studies.

Rothstein cautioned that the studies tested aspirin in patients who had a history of colon cancer or pre-cancerous growths and thus were at high risk for recurrences. Neither examined its potential benefits for average-risk people.

But Rothstein and others connected with the studies said they hoped to find a drug combination - perhaps aspirin and another painkiller - that could deliver greater clout at low risk. Candidates include the so-called Cox-2 inhibitors - arthritis drugs marketed as Celebrex and Vioxx - and calcium supplements.

The new studies appear in today's New England Journal of Medicine.

In a study based at the University of North Carolina, researchers assigned 517 people who had been cured of colon cancer to receive an adult dose of aspirin or a placebo. After a year, polyps were found in 17 percent of the people taking aspirin, compared with 27 percent of those taking the dummy pill.

In the other study, based at Dartmouth University, researchers tested two aspirin doses against a placebo in 1,121 people who previously had benign growths removed. A year into the study, recurrences were detected in 38 percent of the group taking baby aspirin, compared with 45 percent of those taking adult aspirin and 47 percent taking a placebo.

The researchers could not explain why the baby aspirin (an 81 mg. tablet) seemed to prevent recurrences but no significant benefit was seen among volunteers taking an adult dose (325 mg.).

In a commentary published in the medical journal, Dr. Thomas F. Imperiale of the University of Indiana School of Medicine noted that most polyps do not progress to cancer. Because of that, aspirin's risks might outweigh its benefit.

Aspirin's modest effect probably doesn't add much to the proven benefits of colonoscopy exams, which are recommended periodically for anyone with a history of colon problems and once for everyone at age 50.

Dr. Bert Vogelstein, a leading cancer researcher at the Johns Hopkins Kimmel Cancer Center, said a drug that prevents colon cancer is probably more important for average-risk people because patients who have already been treated for the disease should have routine colonoscopies anyway.

So far, such a drug has not emerged. "That doesn't mean that the idea is not very compelling," he said. "And, unfortunately, there is a lot less research on prevention than on treatment."

Dr. Ernest Hawk, chief of gastrointestinal cancer prevention at the National Cancer Institute, said the studies lend support to about 30 previous studies which suggested that aspirin might prevent colon cancer. Many of those found that people who took aspirin for arthritis or other problems developed colon tumors less frequently than did the general population.

"This is one of the more promising approaches in cancer prevention," Hawkes said.

Doctors aren't sure why aspirin prevents growths, but a leading theory is that it reduces levels of an enzyme that encourages cells to divide. The enzyme also blocks the healthy process of cell death.

Hawk agreed that people should not regard aspirin as a substitute for colonoscopies and other screening techniques.

"No one can say that you can take aspirin and forget about screening," he said.

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