CTC Leads to More Follow-Up Colonic Procedures

Despite its safety and having a similar accuracy to traditional colonoscopy, computed tomographic colonography (CTC) in patients symptomatic of colorectal cancer resulted in a significantly higher rate of additional colonic investigation, according to the results of the SIGGAR trial published recently in The Lancet.

“Diagnosis of symptomatic colorectal cancer is a very common problem faced by many medical practitioners,” said investigator Steve Halligan, MD, professor of gastrointestinal radiology at the University College London. “Not all subjects are prepared or able to undergo colonoscopy and we wished to investigate whether CTC was a viable alternative in certain circumstances.”

The SIGGAR trial included 1,580 patients enrolled from 21 hospitals in the United Kingdowm. All patients were aged 55 or older and presented with symptoms that suggested colorectal cancer. Patients were randomly assigned two to one to undergo CTC (n=533) or colonoscopy (n=1,047).

“We found that approximately one-third of patients undergoing CTC were referred for follow-up investigations to confirm or refute an abnormality suspected on CTC,” Halligan said. “Many of these could have been avoided, notably referrals due to small polyps that are not the cause of patient’s symptoms.”

Thirty percent of patients assigned to CTC were referred for additional colonic investigation compared with 8.2 percent of patients who underwent colonoscopy (P<.0001). Patients in the CTC group were reffered to investigate a suspected cancer or polyps of 10 mm or larger (15.6 percent), for smaller polyps (9.2 percent), or due to inadequate examination or clinical uncertainty (5.3 percent).

About 11 percent of patients assigned to both colonoscopy and CTC were diagnosed with colorectal cancer or a large polyp. Overall, CTC missed only one of 29 colorectal cancers and colonscopy missed none.

“CTC is a safe, acceptable, and sufficiently accurate investigation where colonscopy is either not possible or undesirable,” Halligan said. “Clinical guidelines are needed that aim to reduce the referral rate of symptomatic patients following CTC.”

In an accompanying editorial, Otto S. Lin, MD, of the Digestive Disease Institute, Virginia Mason Medical Center in Seattle, Wash., called the results of the study both “reassuring and concerning at the same time.”

Lin pointed to a similar yield rate between CTC and colonscopy, a high yield for large polyps, and the overall safety of the procedure as reassuring aspects, but pointed out that more data are needed on patient satisfaction, cost and feasability.

“If CTC is to become the standard of care, very concrete guidelines about referral for colonoscopy or extracolonic workup need to be defined and implemented,” Lin wrote. “CTC has come a long way since the early studies assessing diagnostic accuracy, but complex cost, capacity, and logistical issues still need to be addressed.”