FDA Panel: Most Favor CTC Colorectal Cancer Screen

Damian McNamara

September 10, 2013

The potential benefits of using computed tomography (CT) colonography to screen asymptomatic adults aged 50 to 80 years for colorectal cancer outweigh the risks, according to most of the 24 members of a joint US Food and Drug Administration (FDA) Medical Device Advisory panel, after they reviewed available evidence.

Unlike many FDA Advisory Panel meetings that culminate in a final vote for or against an approval, the Office of the FDA Commissioner instead sought consensus on the safety and efficacy of CT colonography (CTC) screening because of evolving data. Although widespread agreement emerged on a CTC option, several concerns also arose during yesterday's joint meeting of the Gastroenterology-Urology Devices Panel and the Radiological Devices Panel.

Caveats about patient education and access, physician training, and whether detection of extracolonic findings is a predominantly positive or negative aspect of CTC were discussed.

With no single current colorectal cancer screening strategy universally embraced, many panel members endorsed CTC as an additional option — one that some patients might prefer to optical colonoscopy, fecal occult blood testing, or flexible sigmoidoscopy. The panel intentionally did not address any cost differences between screening strategies.

Mark Talamini, MD, joint panel chair and chief of surgery at the University of California, San Diego, asked whether CTC screening would increase the suboptimal percentage of screened patients. Data show that one third of the US population recommended for screening does not undergo testing.

"Yes, CTC should be one of the options, but I don't think it's going to seriously dent the number of people who will be screened," William Steinberg, MD, a gastroenterologist in private practice in Washington, DC, said.

Duncan Barlow, MD, senior radiologist at Walter Reed Army Medical Center in Bethesda, Maryland, also spoke about compliance. Although not a panel member, he presented experience with more than 15,000 CTCs from the US government's Colon Health Initiative. "We've seen a significant increase in colorectal cancer screenings," he said, but in a subset of 250 patients surveyed after CTC, results showed that "37% would not have gotten screened without CTC available."

"There probably would be an increase in the numbers undergoing screening if CTC is available," said Douglas Coldwell, MD, PhD, from the University of Louisville in Kentucky. However, he added, optimal clinician experience and training, compliance data regarding serial CTC examinations, and the long-term benefits remain unknown.

"It sounds like the panel sees benefit in CTC,...but significant concerns remain," Dr. Talamini said.

Among the few dissenters was Amy Foxx-Orenstein, DO, associate professor of gastroenterology and hepatology at the Mayo Clinic in Scottsdale, Arizona. She said colonoscopy should continue to be presented as an optimal screening tool. "Colonoscopy is by far the best diagnostic and therapeutic tool."

Aline Charabaty, MD, assistant professor of gastroenterology at Georgetown University in Washington, DC, was also less enthusiastic about CTC. "It is very difficult seeing this applied in practice. A patient with positive CTC will have to go through prep again to have the polyp removed," she said. "Another concern is the false sense of safety for patients with relatively normal CTC. They may not return for a recommended 5-year repeat CTC."

Physician Training

There was widespread agreement that additional clinician training is warranted. Leonard Glassman, MD, from Washington Radiology Associates in Washington, DC, said, "In the past panels like this, the FDA mandates training."

Referrals made by nonspecialists was another concern. "Who is going to recommend CTC to the asymptomatic patients?" asked James Ahlgren, MD, from George Washington University Medical Center in McLean, Virginia. "It's not us, it's the general practitioner. How will we get them to appreciate the basics of what is involved?"

Radiation Risk

Most panel members agreed the benefits to screening with this modality outweigh potential radiation risks. "From the safety point of view, the radiation risk from single test given every 5 years is very low," Dr. Kelsen said.

"It sounds like the consensus that is emerging is the benefit of potentially expanding the screening pool outweighs the small risk in this committee's opinion, in general, of the radiation risk," Dr. Talamini added.

Dilemma About Extracolonic Findings

What to do with extracolonic findings in about 10% of patients generated a lot of discussion, specifically of whether CTC picking up other potential concerns outside the colon is primarily a positive or negative feature. It could lead to greater patient anxiety and has the potential for unnecessary surgeries, some argued, but another panel member said that if it saves even a single life, the incidental findings are worthwhile.

"With respect to the extracolonic findings, it feels to me like a wash," Dr. Talamini said. "Half the panel has a great concern, and the other half think there is a great advantage in finding lesions that may not have already been found."

Clinical Trial Evidence

Evidence considered by the panel included a Department of Defense study with 1233 asymptomatic participants. For adenomatous polyps 8 mm or larger, CTC sensitivity was 93.9% and specificity was 92.2%. Optical colonoscopy sensitivity for the same size polyps was 91.5%, and specificity was 92.2%. Lead author Perry Pickhardt, MD, professor of radiology, University of Wisconsin, Madison, said at the meeting that although CTC and OC are comparable, "CTC results in fewer complications, utilizes fewer resources, and results in detection of extracolonic pathology."

Dr. Pickhardt and colleagues also compared parallel CTC and optical colonoscopy screening programs involving 3210 patients at the University of Wisconsin and found similar detection rates.

Abraham Dachman, MD, professor of radiology at the University of Chicago, Illinois, reviewed findings of the American College of Radiology Imaging Network (ACRIN) Trial. In this study of 2531 patients, 390 had abnormal examination findings. The CTC sensitivity for detection of adenomatous lesions 10 mm or larger was 90%, with an 84% specificity.

Edward Dauer, MD, from Florida Medical Services in Fort Lauderdale, said he favors CTC. "All in all, with the evidence seen here today, there is increased patient acceptance and very good sensitivity and specificity."

"CTC has sensitivity at least down to about at least 8 mm, comparable to optical colonoscopy," Dr. Ahlgren said. "The ability of CTC to detect these lesions, I don't think there is really any question about it at this time."

The participants have disclosed no relevant financial relationships.

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