Virtual Colonoscopy Called Cost-Effective If Small Polyps Don't Count

MADISON, Wis., April 23 -- If lesions smaller than 6 mm in diameter are discounted, virtual colonoscopy by a CT scan is more cost-effective than standard colonoscopy, according to researchers here.

A mathematical model shows that virtual colonoscopy is also only slightly less clinically effective in preventing cancer, according to Perry Pickhardt, M.D., of the University of Wisconsin.

The key factor is ignoring the polyps less than 6 mm in diameter, which are unlikely to be neoplastic, Dr. Pickhardt and colleagues reported in the June 1 issue of Cancer.

Virtual colonoscopy is a modality that is evolving rapidly, the researchers said, but it was not known how cost-effective, clinically effective, and how safe it is compared with traditional colonoscopy, the gold standard for colorectal cancer screening.

Earlier research had assumed that patients would be referred for standard colonoscopy for polypectomy if the virtual procedure detected any lesion of any size, Dr. Pickhardt and colleagues said.

But clinical practice, reflecting consensus guidelines, tends to ignore lesions smaller than 6-mm, the researchers said, so they developed a Markov model to evaluate screening methods assuming that those "diminutive lesions" would be ignored.

The model looked at a hypothetical cohort of 100,000 Americans at average risk for colorectal cancer and compared virtual colonoscopy (with and without the 6-mm cutoff), optical colonoscopy, and flexible sigmoidoscopy to no screening at all.

The model showed that no screening resulted in 2,940 cases of cancer, corresponding to a loss of 16,941 life-years and to nearly million in treatment costs, the researchers found.

The model predicted that flexible sigmoidoscopy would reduce the occurrence rate of cancer by 31.4% and standard colonoscopy by 40.4%. Virtual colonoscopy without a size limit -- that is, all lesions were referred for standard colonoscopy and polypectomy -- reduced cancer incidence by 37.8%.

Using the 6-mm cutoff, virtual colonoscopy reduced the cancer occurrence rate by 36.5%.

On the other hand, using the 6-mm cutoff resulted in 12,884 fewer standard colonoscopy procedures with polypectomy -- a 55% reduction. That would also result in 1,112 fewer complications related to the standard colonoscopy -- a 76% reduction, the researchers said.

Cost-effectiveness was measured in cost per life-year gained, compared with no screening, Dr. Pickhardt and colleagues said. Analysis found that:

• Virtual colonoscopy, with the 6-mm cutoff, had a cost per life-year gained of ,361.
• Virtual colonoscopy with no reporting threshold had a cost per life-year gained of ,138.
• Flexible sigmoidoscopy had a cost per life-year gained of ,407.
• Standard colonoscopy had a cost per life-year gained of ,180.

Dr. Pickhardt and colleagues noted that screening for colorectal cancer amounts to a "unique opportunity to actually prevent cancer," but that participation in screening is low, at least partly because patients dislike the screening methods.

"The best screening test for a given individual may well be the test that they are both willing and able to undergo," they said.

The mathematical model shows that small lesions are neither a clinically effective or cost-effective target for screening and that virtual colonoscopy is cost-effective, clinically effective, and safe when those small lesions are ignored.

Virtual colonoscopy should be considered as "an additional effective option to increase overall compliance," the researchers concluded, adding it is "the most cost-effective and safest screening option available."