CT colonography versus colonoscopy for colorectal cancer

Colorectal cancer is the second leading cause of cancer deaths in most developed countries. Screening for colorectal malignancies and polyps (which frequently become cancerous) has been shown to lower the number of deaths from cancer. Most cancer societies and preventive task forces recommend regular screening for cancer of the colon.

Physicians often recommend colonoscopy for screening. Unfortunately, this procedure is uncomfortable and occasionally results in perforation of the colon, sometimes leading to death.

CT colonography is a relatively new imaging technology that can be used to examine the large bowel and rectum where these cancers occur. It is a noninvasive technique that reveals cancer lesions and polyps with nearly the same sensitivity and specificity as colonoscopy, without the risks of bowel perforation.

This study by Heitman and colleagues compares the costs and effectiveness of these two approaches to screening, using assumed prevalences of polyps and cancers among average-risk individuals 50 to 74 years of age. They found that screening 100 000 patients with CT colonography would cost $2.3 million more (in Canadian dollars) than with colonoscopy, and would avoid 3.8 fatal perforations — but at the same time, this method would lead to 4.1 cancer-related deaths from polyps not seen with CT, which would later become malignant. (Colonoscopy is slightly more sensitive than CT colonography, and could be expected to detect a certain number of polyps that the CT method would miss.)

New technologies are always attractive. Because CT colonography does not physically invade the body, it has even more appeal — it is easier for patients to accept. Its cost, however, is much higher, and its benefit (in terms of years of living that are gained) is only slightly lower than when colonoscopy is used.