Aspirin Not a Substitute for Colorectal Screening

November 05, 2001
News Office: Maureen McInaney (415) 502-6397

Some animal studies have shown that aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) have an anti-tumor effect in the colon. Also, some studies in people suggest that these drugs may decrease the risk of colorectal cancer.

However, researchers at UCSF and the University of Michigan have determined in a recent study that aspirin is not a cost-effective addition to the national strategy for reducing death from colorectal cancer.

"While aspirin may be of some benefit in colorectal cancer prevention, it should not replace known screening methods," said Dr. Uri Ladabaum, UCSF assistant professor of gastroenterology and lead author of the study, which appears in the Nov. 6 issue of the Annals of Internal Medicine. "In addition, in terms of cost and benefits, it does not make sense for patients already getting regular screening to take aspirin to prevent colorectal cancer. Screening is highly cost-effective and remains so, even in patients already taking aspirin for other reasons like arthritis or prevention of heart disease."

Screening tests, including flexible sigmoidoscopy every five years and yearly fecal occult blood testing (FS/FOBT) or screening colonoscopy every 10 years (COLO), remain the best strategies for preventing death from colorectal cancer in men and women, according to the researchers.

Though colorectal cancer screening is highly effective, less than half of the population seek it, said Dr. Mark Fendrick, associate professor of medicine at the University of Michigan and a co-investigator on the study. He explained that increasing adherence to screening should be the primary goal on the national agenda for preventing death from colorectal cancer.

"Most colorectal cancers develop from benign growths in the colon called polyps. Screening can detect polyps, and removing polyps can prevent a large fraction of all colorectal cancers," said Ladabaum. "In addition, screening can detect cancers early, before any symptoms have developed. By the time symptoms develop, it is often too late to treat the cancer successfully."

Researchers constructed a computer simulation of the natural history of colorectal cancer in patients at average risk for the disease. In the model, investigators assumed aspirin could reduce colorectal cancer deaths by 30 percent. Aspirin actually increased costs and resulted in loss of life-years when used as an adjunct to FS/BOBT. Under all circumstances, the complications associated with aspirin (bleeding, perforated ulcer and death) were an important determinant of cost effectiveness, according to the researchers.

Aspirin cost $149,161 per life-year gained as an adjunct to COLO. "This is the amount of money that needs to be spent by a third party payer to cover screening, aspirin, cancer care and the complications," said Ladabaum. "In general, interventions that society is willing to pay for are in the range of $50,000 or less per life year gained."

Screening fits within those parameters, he explained. It cost less than $25,000 per life-year gained and was more effective than aspirin alone. In patients already taking aspirin, screening with FS/BOBT or COLO cost less than $31,000 per life-year gained.

"This highlights the need to study safer chemo-prevention alternatives," said Dr. James Scheiman, associate professor of medicine at the University of Michigan and a co-investigator on the study. He added that cyclooxygenase-2 (COX-2) inhibitors may prove to be safer, but more costly.

The computer model estimated clinical and economic consequences of six strategies: 1) no aspirin or screening, 2) FS/FOBT, 3) COLO, 4) aspirin alone (ASA), 5) FS/FOBT and aspirin, 6) COLO and aspirin.

Beginning at 50 years of age, patients progressed through the model for 30 one-year cycles. Principal disease states were defined as: normal, polyp, cancer (localized, regional or disseminated), and deceased. Researchers assumed that 90 percent of cancers develop from polyps and that cancer progresses from localized to regional to disseminated.

Procedure costs were derived from Medicare fee schedules and included professional fees and median procedure reimbursement. Researchers used the wholesale cost of aspirin at the University of Michigan pharmacy. Costs for cancer care of stage-specific colon cancer were taken from reports to the National Cancer Institute. All costs were in 1998 dollars.

This study was funded by grants from the National Institutes of Health to the University of Michigan and UC San Francisco.

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