Screening for colon cancer, but leaving polyps alone
Michael J. Lander
Even if a potential source of trouble is detected, in some instances it may be best to take no immediate corrective action. As researchers led by Dr. Perry J. Pickhardt at the University of Wisconsin Medical School in Madison have concluded, that could be the case for colorectal cancer, a preventable disease that nonetheless claims many lives each year.
With colleagues from University Polo Pontino and from Nuovo Regina Margherita Hospital, both in Rome, the team began the screening study by constructing a mathematical model that included 100,000 hypothetical male and female subjects at average risk for colorectal cancer.
Every 10 years, from the age of 50 to 80, the participants underwent examination for potentially cancer-causing polyps with CT colonography, optical colonoscopy or flexible sigmoidoscopy. CT colonography — the only noninvasive procedure — was modeled both with and without a reporting threshold. With the threshold in place, only polyps with a diameter of 6 mm or greater would be targeted for subsequent removal. Smaller growths, known as diminutive polyps, would remain untreated.
Each technique was analyzed for clinical efficacy, defined as the percent reduction in colorectal cancer incidence compared with no screening. The dollar amount required for a patient to gain an additional year of life also was calculated as a measure of cost-effectiveness.
According to the model, 2940 cases of cancer arose in the population that underwent no screening, resulting in 16,941 life years lost and approximately $98 million in treatment costs. Optical colonoscopy and flexible sigmoidoscopy reduced cancer incidence by 40.4 and 31.4 percent, respectively, while CT colonography without a threshold caused a 37.8 percent reduction. With the 6-mm threshold, the procedure yielded a prevention rate of 36.5 percent.
For every life year gained, CT colonography with nonreporting of diminutive tumors was the cheapest procedure, costing $4361, compared with $7138 for the procedure with no threshold, $9180 for optical colonoscopy and $7407 for flexible sigmoidoscopy.
Although the results indicate that optical colonoscopy could prevent the greatest percentage of colon cancer cases, the method also resulted in 76 percent more complications, such as bleeding and perforation, than CT colonography with a reporting threshold. No one technique was both more clinically effective and more cost-effective than the others.
However, the results suggest that CT colonography’s effectiveness is comparable with that of invasive procedures, reinforcing conclusions that the group drew in a previous study. Although existing guidelines for the noninvasive procedure also recommend the 6-mm reporting threshold, this protocol has seen limited clinical application.
Because the researchers found that nonremoval of diminutive polyps lowered the CT-based technique’s prevention rate by only 1.3 percent and improved its economy drastically, their work may cause the medical community to re-evaluate colon cancer screening procedures.
Cancer, online April 23, 2007, doi: 10.1002/cncr.22668.
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