A study of Medicare patients with osteoarthritis provides additional evidence that non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin reduce the risk of colorectal cancer.
Earlier investigations of the drugs, impact on tumor development could not rule out the possibility that an observed protective effect was caused by other preventive health care measures. The current study, led by a Massachusetts General Hospital (MGH) physician, appears in the August 2007 Journal of General Internal Medicine.
"This is good news for people who take NSAIDs regularly for osteoarthritis," says Elizabeth Lamont, MD, MS, of the MGH Cancer Center, the study's lead author. "Although patients face risks such as bleeding or kidney damage from this therapy, they probably are at a lower risk of developing colorectal cancer." Because of the risks posed by the dosage used to treat osteoarthritis, she and her co-authors stress that currently available NSAIDs should not be used solely to prevent cancer.
Earlier randomized trials clearly showed that NSAID treatment can prevent the development of precancerous colorectal polyps, but whether or not such therapy also reduces the risk of invasive colorectal cancer has not yet been confirmed. Those trials used relatively low doses of aspirin and showed no significant differences in colorectal cancer rates between the aspirin and placebo groups. While many observational studies have shown a protective effect of NSAIDs against colorectal cancer, interpretation of some of those results may have been clouded by other healthy behaviors of the participants.
"It would be ideal to conduct a randomized clinical trial , in which half the patients receive NSAIDs at doses higher than those used in prior trials and half receive placebos , and follow both groups for many years for evidence of cancer. But such trials are expensive, time consuming, and could present real health risks to participants. Therefore, we took advantage of a natural ,experiment, by comparing data from patients known to regularly take higher amounts of NSAIDs with that from those taking lower doses in order to evaluate any effect on colorectal cancer risk."
First the researchers reviewed data from the 1993-94 National Ambulatory Medical Care Survey, in which physicians report on the diagnoses of and treatments prescribed to patients seen during a randomly selected week. Those results verified that older patients with osteoarthritis were more than four times as likely to take NSAIDs as were those without osteoarthritis. They then analyzed information from the Survival Epidemiology and End-Results (SEER)-Medicare program, studying groups of elderly Medicare patients with and without colorectal cancer, to search for associations with NSAID use.
Comparing information on 4,600 individuals with colorectal cancer to data from 100,000 controls, they found that a history of osteoarthritis was associated with a 15 percent reduction in the likelihood of a colorectal cancer diagnosis. A similar association was seen when total knee replacement was used as a marker for NSAID treatment.
"The magnitude of colorectal cancer risk reduction between patients with and without osteoarthritis is completely consistent with the risk reduction for pre-cancerous polyps reported in clinical trials of NSAIDs," Lamont says. "Confirming this association supports the need for further research to identify NSAID agents safe enough to be used for regular, preventive therapy by the general population."