How Aspirin Battles Colorectal Cancer

(Ivanhoe Newswire) -- Study after study has suggested aspirin reduces the risk of colorectal cancer. Now researchers know why.

A new study out of Boston shows aspirin works by blocking the COX-2 enzyme in colorectal tumors -- the same enzyme that causes inflammation and pain in other parts of the body and is one of the main reasons why people take aspirin.

The investigators uncovered the mechanism of action by looking at colorectal cancer cases in about 130,000 male and female health care professionals taking part in larger, ongoing studies. The finding came from dividing colorectal cancer cases found among the participants into two groups: one group had tumors that over-expressed COX-2, and the other had tumors that did not express COX-2 or did so only weakly.

Overall, people who reported taking at least two aspirins a week had about a 75-percent lower risk of getting COX-2 positive colorectal cancer. But they had about the same risk of developing COX-2 negative colorectal tumors as people who didn't take aspirin on a regular basis.

The result was just what the researchers expected to fine. "We knew that aspirin can block COX-2 function and that COX-2 is present in the vast majority of colorectal tumors but not in normal colon tissue," study author Andrew Chan, M.D., was quoted as saying. "Therefore we hypothesized that, if blocking the COX-2 pathway was the mechanism underlying aspirin-associated risk reduction, it should preferentially reduce the incidence of those tumors that rely on COX-2."

He and his fellow investigators stop short, however, of recommending people take aspirin to ward off the cancer. Colorectal cancer screening to find and remove polyps before they turn into cancer is still the best way to prevent the disease.

But they do plan to further study if regular aspirin use might help prevent a recurrence in people who have already had COX-2 positive colorectal cancer.

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SOURCE: The New England Journal of Medicine, 2007;356:2131-2142