New data from two studies are putting virtual colonoscopy in a good light compared with optical colonoscopy. Interim results from a large military study comparing virtual and optical colonoscopy for colorectal cancer screening suggest that the two methods are comparable in terms of sensitivity and specificity. If final results of the 8-year screening virtual colonoscopy (VC) trial confirm this trend, they will be seen as a validation of the landmark 2003 trial that put VC on the map for colorectal cancer screening, suggested by doctor of Walter Reed Army Medical Center in Washington. Speaking at an international symposium on virtual colonoscopy sponsored by Boston University outlined the trial, which includes 3,000 subjects considered to be at average risk in terms of colorectal cancer screening.
The study’s primary goals are to validate the 2003 to evaluate the effectiveness and cost-effectiveness of VC screening in routine clinical practice, and to gather data on the short-term natural history of medium-sized (6-9 mm) polyps. Patients undergoing VC screening are sent to same-day optical colonoscopy (OC) if they have a polyp measuring at least 6 mm (medium size). Patients with fewer than three medium-sized polyps are randomized to either same-day colonoscopy or 1-year VC followup. And patients with no polyps are randomized to either same-day OC or 5-year VC follow-up.
The interim results suggest that for polyps measuring at least 6 mm, VC has a sensitivity of about 90%, compared with about 97% for OC. The specificity found in the 2003 trial, indicating some tendency to identify too many polyps. In a separate presentation, the Mayo Clinic in Rochester, Minn., reported that the miss rate for large advanced neoplasia during optical colonoscopy may be “higher than previously anticipated.” He based his conclusion or comparisons of virtual colonoscopy findings and optical colonoscopy results in a prospective trial of 452 asymptomatic patients who underwent both procedures on the same day. Team noted 43 lesions measuring 1 cm or larger, including 5 cancers and 21 large adenomatous lesions. Seven of these lesions were missed on optical colonoscopy but were seen on virtual colonoscopy. Four of these lesions were cancers measuring 1.3-3.2 cm. There was also 1 tubulovillous adenoma measuring 3 cm, 1 hyperplasic polyp measuring 1.3 cm, and 1 probable leiomyoma measuring 4.4 cm.
Four patients were referred for a repeat colonoscopy, two were recommended for close interval surveillance, and one was observed for new symptoms. The lesions missed on index optical colonoscopy were not confined to any particular colonic segment. Two were located on the proximal aspect of a fold, three were flat, and four were polypoid.