Virtual Colonoscopy May Be Used First in Screening for Colorectal Cancer

October 10, 2007 — Computed tomographic colonography (CTC), also known as virtual colonoscopy, produced similar rates of detection for advanced neoplasia vs optical colonoscopy (OC), researchers report. The results of this large comparative study, which appears in the October 4 issue of the New England Journal of Medicine, suggest that primary CTC along with selective OC should be considered as a preferred screening strategy.
"Virtual colonoscopy is an effective method of colorectal screening, with less risk of complications as compared to optical colonoscopy," said lead author David H. Kim, MD, from the Department of Radiology at the University of Wisconsin, Madison. Seven colonic perforations were observed in the optical colonoscopy group, and 4 patients required surgery to repair the injury. However, there were no perforations or any other serious procedure-related complications observed in the CTC group. "CTC is less invasive and some patients prefer to go this route," he told Medscape Oncology in an interview. "The screening population is a very heterogenous group and some patients prefer one method over another."
"A common question from the referring physicians is why would patients want to have a virtual colonoscopy if they are going to eventually need both," said Dr. Kim. "It seems to be a common misconception."
In reality, most patients undergoing a primary screening CTC would not need to have an OC. "About 87% of test results are negative," he said, "And only 13% are positive, of which only 8% have undergone therapeutic colonoscopy. Thus, only about 8 out of 100 patients would need to undergo both tests."
However, despite the fact that colorectal cancer can be prevented in many cases by removing advanced adenomas before they progress to cancer, screening compliance remains less than optimal. "There are probably 40 million people over the age of 50 that are not screened," said Dr. Kim. "Both methods are going to be needed in order to make a positive impact."
Dr. Kim and colleagues compared the diagnostic yield from parallel studies of CTC and OC by comparing primary CTC screening in 3120 consecutive patients with primary OC screening in 3163 consecutive patients. The main outcome measures were to compare the rates of detection for advanced adenomas and adenocarcinomas, as well as the overall rates for polypectomy.
At the University of Wisconsin, there are 2 clinically established programs for colorectal cancer screening. "We have screening based on CTC which operates independent of screening by traditional optical colonoscopy," Dr. Kim explained. "That's what allowed this study to be done. We have the results of 2 programs that are operating and drawing from the same geographical group of patients, the same referring physicians, and a choice of procedure that was made by the patient in consultation with their physician."
Patients were referred for polypectomy if CTC detected a polyp that was at least 6 mm in size. Those with smaller polyps, in the range of 6 to 9 mm, were also offered the option of continued CTC surveillance as an alternative to polypectomy. Patients who underwent a primary OC had nearly all detected polyps removed during the procedure, regardless of the size of the polyps, in accordance with established guidelines.
A total of 123 advanced neoplasms were detected during CTC, including 14 invasive carcinomas. During OC, 121 advanced neoplasms were detected, with 4 invasive carcinomas. Among patients who received CTC screening, 246 (7.9%) were referred for colonoscopy.
Confirmation of advanced neoplasia was similar between the 2 groups: 100 (3.2%) patients who received primary CTC, and 107 (3.4%) who received primary OC. These numbers did not include 158 individuals with 193 unresected small polyps that were detected on CTC who had chosen to undergo surveillance.
"There is more data than people realize suggesting that surveillance can be done safely," explained Dr. Kim. "If our patients have polyps that are 6 to 9 millimeters, they are given an option — they can have them removed or we offer them imaging surveillance as part of an IRB [Institutional Review Board]-approved research protocol."
The number of polypectomies performed differed significantly between the 2 groups, although the overall outcomes were similar. In the CTC group, a total of 561 polyps were removed vs 2434 among patients who underwent OC.
Currently, screening colonoscopy removes all detected polyps, regardless of the size of the polyps, but with a screening CTC, the patient needs to have a second procedure if a sizeable polyp or multiple polyps are detected, Dr. Kim emphasizes. "If we are able to filter out the patients with high-risk polyps for referral to colonoscopy, we can save on cost, complications, and resource utilization," he continues. "Selection polypectomy strategies at CTC allow removal of high-risk polyps and surveillance for low-risk subgroups. In our study, these strategies allow similar detection yields of advanced neoplasias yet with a marked savings in terms of polypectomies."
Limited follow-up data are currently available for the patients opting for surveillance screening. The majority of patients are awaiting interval CTC examination, and among those with 1 or 2 polyps of 6 to 9 mm, 54 have returned for follow-up CTC with findings of 70 small polyps. Within this cohort, the majority of polyps (96%) were found to have either remained stable or have decreased in size. Only 3 polyps increased in size and were removed, although they did not reach the 10-mm threshold, and on histologic examination, none displayed a high-grade dysplasia.
At the present time, Medicare does not cover CTC for screening purposes, only for diagnostics. However, 1 advantage to not having national reimbursement is that individuals doing research with CTC have been able to really maintain quality, Dr. Kim pointed out.
"As this rolls out, I think that there will be guidelines that make sure physicians are adequately trained, and quality metrics for programs are in place, so that each facility will be held to a certain standard," he said.
Three of the study authors have disclosed various financial relationships with C.B. Fleet, Viatronix, Medicsight, Philips Medical Systems, and AstraZeneca. The remaining study authors have disclosed no relevant financial relationships.
N Engl J Med. 2007;357:1403-1412.