FDA panel: CT colonography a viable colorectal cancer screening option

Issue: October 10, 2013

The FDA’s Gastroenterology-Urology Devices Panel and Radiological Devices Panel found computed tomography colonography to be a viable tool for the diagnosis of colorectal cancer among asymptomatic patients aged older than 50 years in a joint meeting today.

The panel evaluated data from multiple studies of the effectiveness of CTC as a diagnostic tool for colorectal cancer among asymptomatic patients. Across multiple presented studies, CTC yielded sensitivity and specificity ratings similar to those observed with optical colonoscopy (OC) for the detection of adenomatous polyps and colorectal cancer, with higher detection rates for larger polyps.

The majority of the joint panel agreed that CTC was comparable to OC in terms of detection, and that its availability would likely increase the number of patients who undergo screening. Some, however, suggested that adherence to CTC in real-world application would not necessarily mirror that observed in clinical trials. While patients were found significantly more likely to prefer CTC to OC in the incorporated studies, members noted that this might not translate to more frequent screening.

"We know that about one-third of patients in the US are not screened according to guidelines," said James Ahlgren, MD, George Washington University Medical Center in McLean, Va. "There are many reasons those patients are not being screened; the fact that they would prefer some other test is probably not the biggest one. ... But, if there are any patients who will choose CTC and would not otherwise have adequate screening, then we should offer this to them."

The procedure's reduced effectiveness in detecting smaller lesions and flat and serrated polyps, as indicated by the presented data, also was cause for concern among several members. Timothy Nostrant, MD, University of Michigan in Ann Arbor, noted that flat, right-sided lesions often lead to colon cancer as they are commonly missed during screening, and that these lesions were more likely to be missed during CTC.

Participants also assessed the results of risk-benefit analysis for CT use with regard to radiation exposure and “extracolonic findings” – positive results detected on CTC in organs other than the colon. Most members indicated that the radiation-related risk was relatively low and outweighed by the benefits of CTC, and noted both the potential for unnecessary follow-up from false positives due to extracolonic findings, and the benefits of the detection of previously unknown issues.

"The extracolonic findings are the cherry on the top of the sundae for CT colonoscopy," said Leonard Glassman, MD, Washington Radiology Associates in Washington, DC. "They're the life-savers we didn't expect to get ... the person going to the ER knowing they have a right renal stone rather than acute cholecystitis because they were told from this test. Those are plusses, not minuses."

Overall, the panel agreed that CTC administered once every 5 years should be offered as a potential option for CRC screening among asymptomatic patients aged 50 years or older. Several participants suggested that the procedure should be covered by insurance, and many stressed the need for proper training among those who would perform CTC, as well as the implementation of quality control procedures including accreditation for facilities administering CTC or the development of a registry of CTC recipients.

"Given all that we've heard today and all that I know about the subject, CTC should be one of the options available," said Abdelmonem A. Afifi, PhD, School of Public Health at UCLA in Culver City, Calif. "Having said that, I also think that primary care physicians need to be quite well educated; most of the time, they're the ones making the recommendation."

According to FDA acting associate commissioner for policy and planning Peter Lurie, MD, MPH, the results of the meeting will be provided to the FDA's center for devices and radiological health in order to inform their continued regulation of CTC.