Radiology: CTC may be more suitable for initial colorectal screening

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CT Colonoscopy

A systematic review of nearly 50 studies revealed that CT colonography (CTC) yields comparable sensitivity to colonoscopy, leading the authors to suggest that CTC might be a more suitable initial exam for suspected colorectal cancer, according to a study published in the May issue of Radiology.

CTC has become an increasingly common alternative to colonoscopy, with many providers expressing the hope that the less invasive CTC could improve sluggish compliance with colorectal cancer screening guidelines among the general public. Substantial debate has persisted over CTC, however, with some studies suggesting that the exam provides inferior cancer detection, particularly for smaller lesions, resulting in Medicare’s highly controversial rejection of coverage for CTC screening for colorectal cancer.

In the present study, the authors performed a systematic review and meta-analysis to assess the sensitivity of CTC and colonoscopy. The researchers considered all studies that compared the two exams between 1994 (marking the introduction of CTC screening) and the end of 2009.

After excluding studies for conditions such as lack of histological confirmation or study bias, the authors reviewed 49 studies, comparing the cancer detection rates for CTC and colonoscopy among 11,551 individuals.

“Our meta-analysis shows that the pooled sensitivities of CT colonography and [colonoscopy] for colorectal cancer were about 96 percent and 95 percent, respectively,” explained Perry J. Pickhardt, MD, from the department of radiology at the University of Wisconsin School of Medicine and Public Health in Madison, and co-authors.

A total of 414 colorectal cancers were discovered among the 11,551-person meta-analysis. Three hundred ninety-four of these cancers were observed in disease-enriched studies, whereas just 20 cancers were detected among the 4,883 individuals who underwent colorectal screening via the two modalities.

CTC depicted 398 of 414 histologically confirmed cancers, with an interstudy heterogeneity of 0 percent. Among the 25 studies examining cancer based on colonoscopy only, followed by colonoscopy plus knowledge of CTC findings, colonoscopy visualized 178 of 188 cancers. Interstudy heterogeneity for these colonoscopy findings was 50 percent, due primarily to one study that measured colonoscopy sensitivity at 20 percent.

The majority of the 16 cancers missed by CTC were located in the rectosigmoid colon (10, six of which were in the rectum), followed by six masses located in the proximal splenic flexure.

“When one considers the large number of cancer cases included, the wide range in CT colonography techniques used and the lack of heterogeneity in the CT colonography sensitivity estimate, our study results support the clinical equivalence between CT colonography and [colonoscopy] for the detection of invasive cancer,” Pickhardt and colleagues wrote.

Pickhardt and co-authors further argued that their wide inclusion criteria provided a representative sample of CTC usage in the U.S. and abroad. For example, by reviewing studies that used single- and multi-detector CT scanners, various contrast protocols and no single imaging position (e.g., supine vs. prone), Pickhardt and colleagues may have provided a more realistic evaluation of CTC as used in clinical practice.

“Despite this considerable variability in CT colonography techniques, there was very little heterogeneity in the sensitivity data, implying that CT colonography is a highly robust method for cancer detection, regardless of the specific technique used,” the authors contended.
The researchers pointed out that their data might have led to an underestimation of CTC’s sensitivity for approximately half of the studies reviewed, because the use of colonoscopy as the standard might have labeled CTC findings as false-positives, when in fact the colonoscopy results could have been false-negatives, or misses of cancer that CTC correctly detected.

Pickhardt and colleagues concluded that, “Given the relatively low prevalence of colorectal cancer, even among symptomatic cohorts, our findings suggest that, assuming a reasonable level of specificity, primary CT colonography may be more suitable than [colonoscopy] for the initial investigation of suspected colorectal cancer.”