A daily aspirin may lower the odds of developing colon, prostate and breast cancer for people at high risk for those malignancies, researchers at the American Cancer Society (ACS) report.

"Men and women who used adult-strength aspirin daily for five or more years had about a 15% lower overall rate of developing cancer, particularly colon, prostate and possibly breast cancer," said study lead author Dr. Eric Jacobs, an epidemiologist at the ACS.

However, his team said there's not enough evidence that aspirin's value as a cancer preventive outweighs its potential toxic side effects, which include a higher risk for bleeding.

The Study

In the study, researchers looked for a link between long-term aspirin use—dosed at 325 milligrams or more a day-and cancer in nearly 70,000 men and more than 76,000 women.

During 12 years of follow-up, more than 18,000 men and women were diagnosed with cancer.

The researchers found that taking daily aspirin for at least five years was linked with about a 15% relative reduction in overall cancer risk. This decrease did not reach statistical significance in women, however.

In addition, aspirin was associated with a 20% reduction in the risk for prostate cancer in men and a 30% reduction in the risk for colorectal cancer in both men and women, compared with people who didn't take the medicine, Jacobs's team found.

Aspirin had no effect on risk for lung cancer, bladder cancer, melanoma, leukemia, nonHodgkin's lymphoma, pancreatic cancer, and kidney cancer, the researchers noted. Also, aspirin use for less than five years did not lower the risk for cancer.

More Research Needed

If more evidence comes to light suggesting that aspirin curbs cancer risk, American Cancer Society recommendations might someday change, Jacobs said. "Future recommendations could take cancer prevention into account when deciding on the best dose for people who already need to take aspirin for cardiovascular protection," he said. "We're not there yet."

Expert Reaction

One expert agreed that aspirin should not be taken to prevent cancer, at least for now.

"The jury is still out about making recommendations about aspirin for the prevention of cancers. Even those cancers where we do see significant protection," said Dr. Maria Elena Mar tinez, from the Arizona Cancer Center, Tucson.

It is difficult to make recommendations when there are significant toxicities associated with aspirin, Martinez said. "People should not take aspirin for the protection against colon cancer or any cancers at this point," she said.

Martinez said that unlike cardiovascular protection—where low-dose aspirin appears to be effective—cancer protection is only seen when high doses are taken. "It's with the higher doses where we see the toxicity and side effects," she said.

"If there were evidence that aspirin protected against a multitude of cancers, then we might get to the point where we say it's time to start considering it," Martinez said. "But you have to keep in mind that it comes with side effects. At this point, we are not ready to say, "Take aspirin,' as we do with cardiovascular disease," she added.

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