Aspirin No Colon Cancer Panacea

A large study of women weakens hopes that low doses of aspirin could be an easy way to prevent colorectal cancer.

Aspirin helps, but its effect is significant only after a decade of use, according to a 20-year study of almost 83,000 nurses published in Wednesday's Journal of the American Medical Association.

Low doses of aspirin did not lower cancer risk significantly. High doses of aspirin — such as two or more aspirin per day — reduced colon cancer risk by a third, but also were linked to dangerous bleeding.

"The hope was we might be able to find something, like aspirin, that would protect a large segment of the population," study co-author Dr. Andrew Chan, a researcher at Harvard Medical School,

"We found regular aspirin use in general does seem to protect against colon cancer, but it looks like (it was women on) the highest doses, women taking more than 14 standard aspirin tablets a week, who enjoyed the greatest benefit."

A high-dose aspirin regimen that prevented one or two cases of colorectal cancer also would cause eight additional cases of serious bleeding from irritation of the stomach or intestines, the researchers estimated.

"We can't make a recommendation that you could take an aspirin a day to prevent both heart disease and colorectal cancer," said Chan.

"Research suggests aspirin works," he told Smith. "Again, there are trade-offs from taking aspirin at these higher doses. So it may not be the answer, even for people at greater risk."

That said, "There still may be some people in the population who have particular risks who may decide that weighing the risks and benefits with the physician, it might make sense, but that has to be looked at."

He tells CBS News, "One of the exciting things about the study is to show that aspirin or aspirin-like drugs can prevent cancer. It does suggest that there is an opportunity for the development of future treatments that hopefully don't have the same side effects as aspirin."Even if we can't put the findings into widespread use now, we are learning more about how colon cancer works, and it does provide hope for the future that we're able to develop better options for people."

The best prevention is regular screening, exercise and eating a high-fiber, low-fat diet, Chan and other researchers not involved in the new study said.

"For average-risk people who are getting screening colonoscopies, the added benefit of taking aspirin is very small," said Dr. Robert Sandler at the University of North Carolina-Chapel Hill. Sandler was not involved in the study.

In addition, Chan tells CBS News, "Our study focused on aspirin, but it wasn't surprising that we found that non-steroidal anti-inflammatory drugs (NSAIDs) also were effective. We didn't specifically ask individuals what kind of NSAID they were using, but the most common one was ibuprofen. Ibuprofen and aspirin do show similar effects."

Previous studies suggested that a once-a-day baby aspirin could prevent precancerous polyps that sometimes become colorectal cancer, the second deadliest cancer for Americans after lung cancer.

Those prior studies raised hopes that the same small dose of aspirin shown to fight heart disease could do double-duty against cancer. Aspirin might inhibit an enzyme linked to tumor formation.

Long-term use of high doses of aspirin are not right for most people, cautioned Dr. Julie Buring of Harvard's Brigham and Women's Hospital, who has conducted similar research but was not involved in the new study.

Buring published a study last month showing that women who took low doses of aspirin over 10 years had no lower risk of colorectal cancer and several other cancers.

"This would not be something you would choose to do on your own," she said. "If we're talking about high doses over long periods, you have to talk to your doctor for this."