WEDNESDAY, May 23, 2007 (HealthDay News) -- Aspirin can reduce the risk of a common form of colon cancer but not all forms of the disease, new research suggests.
The study found that regular use of aspirin lowered the risk of colon cancer associated with expression of the cox-2 enzyme. This type of colon cancer accounts for about two-thirds of the colon cancer cases in the United States, according to the study.
However, the study authors aren't recommending that people start using aspirin for colon cancer prevention just yet.
"Although studies have been very supportive for the potential benefit of aspirin, it still remains unclear who stands to benefit the most," said the study's lead author, Dr. Andrew Chan, an assistant professor of medicine at Massachusetts General Hospital and Harvard Medical School in Boston. "It's important to determine if there are individuals that will benefit significantly enough to outweigh the potential risks of gastrointestinal bleeding."
Part of the problem is that there's currently no way to know who's at risk for cox-2-expressing colon cancers, and aspirin had little effect on colon cancers that didn't express the cox-2 enzyme. That means that for about one-third of people with colon cancer, aspirin wouldn't help to prevent the disease and could cause unnecessary side effects.
The new study findings are published in the May 24 issue of the New England Journal of Medicine.
Each year, more than 140,000 Americans are diagnosed with colon cancer, and the disease claims nearly 56,000 lives annually, according to the U.S. Centers for Disease Control and Prevention.
Chan explained that past research had found an association between aspirin use and lower rates of colon cancer, but why aspirin might affect colon cancer rates wasn't clear.
To further investigate how aspirin might help to reduce the risk of colon cancer, Chan and his colleagues used data from the large Nurses Health Study and the Health Professionals Follow-Up Study. These databases had information on aspirin use and the incidence of colon cancer for almost 83,000 women and more than 47,000 men.
Between those databases, there were 636 cases of colon cancer with available tumor samples. The researchers found that 67 percent of the tumors had moderate or strong cox-2 expression. Cox-2 is an enzyme that causes inflammation in the body.
Regular aspirin use, which for this study was defined as a standard adult dose (325 milligrams) twice or more per week, reduced the risk of a cox-2-expressing colon cancer by 36 percent. Aspirin reduced the risk of non-cox-2 colon cancers by 4 percent, according to the study.
"This study shores up the point: Aspirin use -- if it's regular and cumulative -- reduces the burden of colon cancer with cox-2 expression," said Dr. Samir Gupta, an assistant professor of internal medicine at the University of Texas Southwestern Medical Center at Dallas.
"This adds to the debate as to whether everyone should get aspirin for colon cancer prevention and the question of how you balance the risk of bleeding against the potential protective effects against colon cancer and cardiovascular disease," said Gupta.
"The dose required for colon cancer prevention is higher than the dose required to protect against heart disease, and that's problematic," he added.
Both Chan and Gupta said that aspirin isn't recommended as a preventive measure for colon cancer, but that this study will likely spur research to identify who's at risk of cox-2-expressing colon cancers and for new drugs that can provide aspirin's benefits for colon cancer without the risks associated with the drug.
In the meantime, Chan emphasized that colon cancer screening beginning at age 50 is a known way to prevent the disease, because precancerous polyps can be detected and removed during a colonoscopy.
More information
To learn more about ways to prevent colon cancer, visit the National Cancer Institute.
