TUESDAY, April 17 (HealthDay News) -- A daily aspirin may lower the odds of colon, prostate and breast cancer for people at high risk for those malignancies, researchers at the American Cancer Society report.
"Men and women who used adult-strength aspirin daily for five or more years had about a 15 percent lower overall rate of developing cancer, particularly colon, prostate and possibly breast cancer," said study lead author 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.
For that reason, the study raises more questions than it answers, Jacobs said.
"There really aren't any immediate clinical implications," he said. "The American Cancer Society doesn't recommend using aspirin to prevent cancer, because aspirin can cause serious gastrointestinal bleeding," he added.
His team published its findings in the April 17 issue of the Journal of the National Cancer Institute.
In the study, they looked for a link between long-term use of aspirin use -- dosed at 325 milligrams or more a day -- and cancer in almost 70,000 men and more than 76,000 women participating in the Cancer Prevention Study II Nutrition Cohort.
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 percent relative reduction in overall cancer risk. This decrease did not reach statistical significance in women, however.
In addition, aspirin was associated with a 20 percent reduction in the risk of prostate cancer and a 30 percent reduction in the risk of 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 of lung cancer, bladder cancer, melanoma, leukemia, non-Hodgkin'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.
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."
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 Maria Elena Martinez, from the Arizona Cancer Center, Tucson, and the author of an accompanying journal editorial.
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 cardio 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.