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Baby Aspirin Better for Cutting Colon Cancer Risk

Less is more in preventing pre-cancerous growths, Dartmouth research reveals

SUNDAY, April 7 (HealthDayNews) -- Smaller doses of aspirin work better than larger doses in reducing the risk of pre-cancerous growths in the colon, a group of Dartmouth researchers reported today in the first study of its kind.

The research, which tested baby aspirin against standard adult aspirin in patients at increased risk for colon cancer, was presented at the 93rd annual meeting of the American Association of Cancer Research in San Francisco.

"The fact that we found activity in suppressing adenomas [pre-cancerous growths] is certainly very encouraging ... although we were very surprised by the fact that the smaller doses of aspirin worked better than the larger ones, and we don't really understand why," say study author Dr. John A. Baron, a professor of medicine at Dartmouth Medical School in Lebanon, NH.

Adenomas -- also known as polyps -- start out as benign growths that develop in the lining of the colon. Although not all polyps are considered adenomas, those that are are believed to be precursors to cancer. If not removed, adenomas can become extremely aggressive, and they can eventually result in colorectal cancer.

Although epidemiology studies have long shown that aspirin may protect against colon cancer by reducing the risk of adenomas, this was the first study to examine which dosages might work best, particularly for those already at increased risk.

"Overall, we found that, in those people who already had one adenoma removed, aspirin definitely had a protective effect, and moreover, those who had the most aggressive adenomas had the greatest margin of protection, and from the smallest dose of aspirin," Baron says.

The aspirin doses used in the study were 80mg daily (the equivalent of one baby aspirin) and 325mg daily (equal to one standard aspirin). The dosages were chosen, says Baron, because they reflected what people were already taking for cardiovascular protection.

For gastroenterologist Dr. Carl McDougall, that line of thinking makes good sense, and he calls the study finding important.

"Overall, this is a very good study with some very good news, because it means that people may be able to get the protective effects of aspirin, even if they are not able to take large amounts," McDougall says.

But he does note that because the study is a first to look at different doses, that automatically limits the impact of the finding.

"I'd like to see this kind of study confirmed independently . . . You really need to see these results duplicated before you can say for certain that lower doses work best for preventing these adenomas," says McDougall, an associate professor of clinical medicine at New York Weill Cornell Medical Center.

And, he adds, because this study included only those people who already had had adenomas, it's hard to know whether the smaller doses would be equally effective in protecting against the initial development of these lesions, or if larger doses might work better for this group.

Because aspirin, particularly in larger doses, can be problematic for some people, the new study began with a pre-trial test to check for tolerance. To do this, potential study candidates were asked to take 325mg of aspirin daily for three months, and to note any significant side effects.

Choosing from among those who did not have any adverse reactions, researchers selected 1,121 men and women who had had at least one previous adenoma surgically removed. All were randomly assigned to take either 80mg of aspirin per day, 325mg of aspirin per day, or a placebo, for a period of 34 months.

When the results were analyzed, those taking 80mg a day reduced their risk of a recurrent adenoma by 19 percent compared to those taking the placebo. Those taking 325 mg a day saw only a 4 percent reduction in risk.

In further analysis that compared the types of adenomas initially removed (from mildly aggressive to very aggressive), the data suggested the low-dose aspirin had the highest risk reduction.

In those patients who had previously experienced the most aggressive lesions -- known as tubulovillous or villous adenomas -- baby aspirin cut the risk by some 40 percent. The higher-dose aspirin reduced the risk by only 19 percent.

Although the study doesn't say that aspirin prevented colon cancer, Baron notes that it is consistent with previous data that shows cutting the risk of adenomas decreases the risk of cancer.

"The fact that we found activity in suppressing adenomas is certainly very encouraging and certainly very consistent with the epidemiology," Baron says.

Colorectal cancer is a major health concern, affecting up to 150,000 Americans annually, and killing 56,000 each year. In addition to aspirin, the latest studies have shown that taking 1,200mg daily of calcium carbonate ( the kind found in most calcium supplements) may also reduce the risk of colorectal cancer. Although fiber was once thought to have protective effects, further studies have shown this may no longer prove true.

What To Do

To learn more about colon cancer, including symptoms and the latest treatments, visit The Cancer Research Foundation of America .

For more information on current clinical trials involving colon cancer, visit Oncolink .

To learn more about the power of aspirin to prevent disease, check out The Aspirin Foundation.

SOURCES: John A. Baron, M.D., study author, professor of medicine, Dartmouth Medical School, Lebanon, NH; Carl McDougall, M.D., associate professor of clinical medicine, New York Weill Cornell Medical Center, New York City; April 7, 2002 study presentation, American Association of Cancer Research annual meeting, San Francisco
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