Taking aspirin regularly may help treat colorectal cancer in some patients, according to a new study in JAMA. However, experts say that data, while promising, isn't conclusive and caution patients to talk to their doctor before taking the medicine cabinet staple.

"This study found aspirin may be helpful as a treatment for some colorectal cancer patients. While the findings are encouraging, this is just one study and it wasn't randomized. We're awaiting confirmation from other studies before we change our recommendations to the public," says Durado Brooks, MD, director of colon and prostate cancer prevention programs for the American Cancer Society (ACS).

What the researchers found

The study, led by Andrew T. Chan, MD, MPH and colleagues from Massachusetts General and Harvard Medical School, was based on nearly 12 years' worth of follow-up data from 1279 colorectal cancer patients enrolled in 2 large prospective studies, the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS).

It found that colorectal cancer patients who took aspirin regularly lowered their risk of dying from the disease by 29% and were 21% less likely to die overall, compared to patients who didn't take the drug.

New aspirin users, those with COX-2 tumors benefitted most

Aspirin's benefit was greater among patients who didn't take the drug before their diagnosis, and among those with tumors that overexpress COX-2, an enzyme that's associated with inflammation and cell growth. COX-2 is elevated in up to 85% of colorectal cancers, and many researchers think it might hold the key to better understanding and treating colorectal cancer. Aspirin inhibits the behavior of COX-2.

The benefits held regardless of whether the patient had chemotherapy or not, and regardless of whether they were stage I, II, or III at diagnosis.

This study did not look at aspirin's effects in people with advanced colorectal cancer. More research in that area is needed.

It also didn't address the preventive effects of regular aspirin use. Other studies have shown that aspirin may reduce the risk of colorectal polyps and associated cancer.

"However, the use of aspirin to prevent colorectal cancer is not recommended by the American Cancer Society and other medical groups because those benefits are offset by the potential risks of gastrointestinal bleeding. The recommendation for the use of aspirin to prevent disease is based entirely on the prevention of heart disease," says Michael J. Thun, MD, MS, American Cancer Society, vice president emeritus of Epidemiology and Surveillance Research.

Regular aspirin use has been shown to offer cardiovascular benefits and help ward off heart disease.

Aspirin's dangerous side effects

Before you start taking aspirin, consult your doctor. Taking aspirin regularly can have serious side effects, including stomach bleeding and irritation. People with a history of gastrointestinal problems are at especially high risk for these problems, but they can occur in anyone.

The best way to prevent colorectal cancer is to get regular tests for the disease. People who have no identified risk factors should begin regular screening at age 50. Those who have a family history or other risk factors for colorectal polyps or cancer, such as inflammatory bowel disease, should talk with their doctor about starting screening at a younger age and/or getting screened more frequently.

For more information on how to prevent and treat colorectal cancer, see Detailed Guide: Colon and Rectum Cancer.

Reviewed by: Members of the ACS Medical Content Staff

Citation: "Aspirin Use and Survival After Diagnosis of Colorectal Cancer." Published online August 12, 2009 in JAMA. First author: Andrew T. Chan, MD, MPH, Massachusetts General Hospital.