"There are insufficient data to determine which strategy is best in terms of the balance of benefits and potential harms or cost-effectiveness," the panel said. "Studies reviewed by USPSTF indicate that colorectal cancer screening is likely to be cost-effective (less than $30,000 per additional year of life gained) regardless of the strategy chosen."
In deciding which screening strategy to choose, physicians should consider a patient’s preference, medical contraindi-cations, patient adherence, and the resources available for testing and follow-up, the panel added.
Moreover, it found no direct evidence by which it could determine optimal intervals for screening tests save for FOBT, which reduces mortality more when used annually than every 2 years. Nor could the panel determine an age at which to recommend discontinuing screening for colorectal cancer.
Although FOBT and sigmoidoscopy combined may find more tumors and larger polyps than either technique used alone, the additional benefits and risks of doing the two screenings together remain uncertain, the USPSTF said. When both are used, FOBT should generally precede sigmoidoscopy because a positive FOBT indicates the need for colon-oscopy.
"There is little evidence to determine the effectiveness of either digital rectal examinations [DREs] or a single office FOBT using a stool sample obtained on DRE," the panel said.
Colonoscopy is a more sensitive and specific test for colorectal cancer and large polyps than other screening techniques, but it also carries higher risks, including a small danger of bleeding and perforation of the bowel, the panel said. "It is not certain whether the potential added benefits of colonoscopy relative to screening alternative are large enough to justify the added risks and inconvenience for all patients," the report stated.
The panel further noted that the accuracy of colonoscopy is difficult to evaluate because the procedure is usually considered the criterion standard, and its specificity is also difficult to define. "Many patients will have polyps detected or removed on colonoscopy, but only a minority of those would have developed cancer," the report stated.