Virtual colonography less cost-effective than stool tests

Virtual colonoscopy is more effective than not screen-
ing, but more costly and less effective than stool test
with sigmoidoscopy, and colonoscopy.
(photo used by permission of RSNA)

MADISON, WI – (Cancer Digest) –There’s no perfect colorectal cancer screening method, but if cost-effectiveness is one of your considerations, the least invasive is also the least cost-effective, according to a new study.

Led by Dr. David Vanness, assistant professor at the University of Wisconsin School of Medicine and Public Health, the researchers compared the cost-effectiveness of CT colonography for colorectal cancer screening in average-risk asymptomatic subjects in the United States aged 50 years. The study was published this week online in the journal Radiology.

The screens they compared included the long-used stool test along with a newer immunochemical version both coupled with a sigmoidoscopy. They also looked at the “gold standard” colonoscopy and compared costs and effectiveness of these three methods in detecting and ruling out cancer with the costs and effectiveness of CT colonography, often called a virtual colonoscopy.

Vanness told Cancer Digest that each of the tests have strengths and weaknesses.

“Stool testing has been around a long time. It is noninvasive and cheap but it misses precancerous adenomas, so it has limited value by itself,” Vanness said in a phone interview. “Ususally it is done in combination with flexible sigmoidoscopy, which is invasive, its limitation is that it only reaches the lower one third of the colon, if you have any lesions above that you miss them. So it is an incomplete method by itself.”

Colonoscopy, he said is a very invasive and expensive procedure that requires sedation and recovery time. It is considered the gold standard, but it is not perfect, small polyps or lesions that are hidden in anatomically difficult places can be missed.

“And virtual colonoscopy is non-invasive, uses imaging to reconstruct three- and two dimensional images of the colon. It is pretty accurate in detection of precancerous adenomas and carcinomas, but in clinical studies of its performance it is not clear whether the performance is comparable to other methods and what the effects of those differences in detection would mean long-term,” he said.

In the study Vanness and colleagues used three statistical models to re-analyze the data from the largest study to date to look at CT Colonography performance, the ACRIN 6664 protocol of the National CT Colonography Trial. That trial was designed to determine clinical detection accuracy of the three screening methods.

In the current study Vanness said that what matters at the patient level is whether a virtual colonoscopy results in referring patients with precancerous lesions to the appropriate follow-up and treatment as needed. He said they use the statistical models because it takes 10 to 20 years to complete long-term screening studies.

They compared each method assuming either 100 percent of the population would follow current screening guidelines or 50 percent of the population would follow them.

When they assumed 100 percent of the population would adhere to screening guidelines all models found that colonoscopy, the fecal immunochemical test plus flexible sigmoidoscopy, and fecal occult blood test plus flexible sigmoidoscopy increased life expectancy and reduced lifetime colorectal cancer risk more than CT colonographic screening at 5- or 10-year intervals.

When they assumed 50 percent of the population would adhere to screening guidelines, performing CT colonography every 5 years reduced colorectal cancer risk more than colonoscopy in two of the three models. Under one model the risk was reduced by 39.1 percent compared to 38.7 percent for colonoscopy. In the other model the risk reduction was 61.6 percent compared to 59.5 percent.

When they looked at cost with 100 percent participation, CT colonography every 5 years was the most expensive, ranging from and average of $2,900 to $3,854. At 50 percent participation all simulations found CT colonography every 5 years was the most expensive.

Vanness said that while all three models varied in terms of absolute costs and outcomes, they were consistent in ranking the three screening methods in terms of relative costs, outcomes and net benefits.

The bottom line, Vanness says is that researchers need to continue to work to find better, more widely accepted screening methods. Until then, it is important to get screened.

“Economic efficiency is not the only consideration. So just reaching a segment of the population that would not otherwise get screened is important,” Vanness said. “We need to continue to look at more and better ways to improve screening. Whether it is DNA fecal occult test, or reduced preparation, or prep-less CT colonography, all need to be developed. In the meantime, the one thing all the models agree on is that screening is important.”