Computed tomography imaging colonography may be a better method for primary colorectal cancer screening than optical colonoscopy, according to the authors of a study published Oct. 4 in the New England Journal of Medicine.

Results of the 6,283-patient non-randomized study by David Kim, M.D., et al., University of Wisconsin, show that optical colonoscopy requires the removal of more polyps to yield the same number of potentially cancerous polyps as found with CT colonograpy.

In the study, 123 neoplasms were removed from 100 patients in the CT group and 121 neoplasms were removed from 107 patients in the colonoscopy group. Physicians removed 2,434 polyps in the optical colonoscopy group, versus only 561 in the CT group.

Importantly, both groups yielded the same number of advanced adenomas. Advanced adenomas are small subsets of polyps that are benign by themselves but often become cancerous over time. Advanced adenomas are therefore the optimal target lesion for therapies intended to prevent colorectal cancer, according to the authors.

Kim and colleagues argue the best strategy for colorectal cancer screening might be to start with CT screening to identify potential advanced adenomas and then use traditional colonoscopy to remove those polyps and confirm they are precancerous.

CT colonography may also be a better primary screening method because it is better than colonoscopy at distinguishing "diminutive" polyps (less than 5 mm), which are rarely dangerous, from larger polyps that are more likely to become cancerous, the authors argue.

In the study, physicians ultimately removed 2,006 diminutive polyps from the colonoscopy group and only four (0.2%) were found to be advanced lesions. According to the authors, this finding suggests that a strategy of not reporting diminutive polyps detected in CT screening would be a cost-effective approach that could substantially reduce the need for polypectomy and risk of complications without a difference in cancer detection.

The study also showed CT to be slightly safer than colonoscopy. In the study, there were no serious adverse events in the CT group while there were colonic perforations in seven (0.2%) patients in the colonoscopy group, including four requiring surgical repair.

The researchers point out that some patients will be more willing to have a less invasive CT exam than a colonoscopy, which could increase patient compliance to recommended screening intervals.

The authors acknowledge the study's lack of randomization as "a major limitation," and note that there may have been a differentprevalence of advanced adenoma in the two groups that could skew the results. Both groups had an average age of about 58 and were around 56% female, but the number of confirmed cancerous lesions found in the CT group was much higher than in the colonoscopy group - 14 versus 4.

The American College of Gastroenterology cited these limitations in an Oct. 4 statement to patients on the clinical significance of University of Wisconsin study. "We need additional information to interpret this nonrandomized comparison before we can generalize the results to clinical practice," ACG President David Johnson, M.D., Eastern Virginia Medical School.

Further evidence supporting CT colonography as a primary screening test for colorectal cancer may come from the National Institutes of Health-supported National CT Colonography Trial. Run by the American College of Radiology Imaging Network, the trial is the largest study of primary cancer screening with CT colonography to date, enrolling more than 2,500 asymptomatic patients at 15 centers in two years.

According to preliminary findings released last month at the ACRIN 2007 meeting in Arlington, Va., the trial shows that virtual colonoscopy is "highly accurate" for detection of intermediate and large polyps. The formal study results have been submitted for publication and will be presented in greater detail in the coming months, according to E-Z-EM, manufacturer of the Protoco2l carbon dioxide insufflation system and the Tagitol V tagging contrast used in the study.

- Reed Miller (re.miller@elsevier.com)

NEJM Study Supports CT Colonography As Primary Colon Cancer Screen

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