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Virtual colonoscopy shows significant promise as colorectal cancer screening option


Though many issues need to be addressed

A future trends report published today in the American Gastroenterological Association’s journal Gastroenterology, concludes that CT colonography (often referred to as "virtual colonoscopy") has significant promise. However, the technology is still evolving and the results of CT colonography for screening are variable.

Guidelines of multiple agencies and professional societies underscore the importance of screening for all individuals 50 years of age and older. Currently, there are a number of tests that may be used to screen for colorectal cancer, the second-leading cause of cancer deaths in the United States. Approved tests include barium enema, fecal occult blood test, flexible sigmoidoscopy and colonoscopy. Each screening option has advantages and disadvantages.

"No colorectal cancer screening test is perfect. CT colonography is currently not the most accurate or convenient test, but may in the future be included in the mix of colorectal cancer screening options available to patients and physicians," says AGA President Emmet B. Keeffe, MD. "While the virtual aspect of the test sounds appealing, it isn’t a panacea. CT colonography is associated with discomfort and still requires rigorous preparation, often the most daunting challenge to compliance. Many practical issues still need to be addressed, including standardization of test performance, patient preparation and interpretation of test results before CT colonography can be recommended for routine clinical practice. The shortage of radiologists in the country confounds the issue of training a sufficient supply of physicians able to deliver care to patients on a widespread and consistent basis."

As a service to AGA members and their patients, the AGA assembled a task force of gastroenterologists, radiologists and epidemiologists to undertake a critical analysis of available information on the capabilities of CT colonography and to consider its potential role in colorectal cancer screening. The task force reviewed the results of recent clinical trials and quantitative mathematical models pertaining to CT colonography. Limitations in the evaluation of CT colonography included variation in results of clinical trials and limited data on its use in routine clinical practice.

One limitation of CT colonography is that the test cannot consistently detect flat polyps or those smaller than one centimeter. The clinical importance of these types of polyps remains largely uncertain but given that a small number might harbor malignancy, most clinicians advise their removal. Thus a significant proportion of patients undergoing CT colonography might need a second procedure if it is necessary to remove all small growths. Fundamental questions currently without answers based in clinical outcomes studies include:

Is there a minimum polyp size detectable by CT colonography for which patients should be referred for polyp removal?

What is the minimum-sized lesion by which CT colonography sensitivity should be judged?

What polyp size, if any, would physicians and more importantly their patients, allow to remain in place and undergo surveillance rather than immediate removal?

How will CT colongraphy screening followed by colonoscopy for patients with polyps impact patient compliance and health-system costs?

"There is little doubt that effective screening for polyps with the hope of preventing the development of colorectal cancer is among the most important health problems for our society, and clinical challenges for gastroenterologists," notes Daniel K. Podolsky, MD, immediate past president of the AGA. "The need to define the natural history and biological significance of polyps smaller than a centimeter is central to refining colorectal cancer screening, irrespective of modality."

One of the largest barriers to patient compliance for colorectal cancer screening is the bowel cleansing preparation required prior to the test. Patients must undergo similar bowel preparation for CT colonography as they do for traditional colonoscopy. However, progress is being made in the development of a minimal prep or prep-less CT colonography examination. Improvements in CT colonography stool tagging to "electronically cleanse" the colon are not yet available for clinical use.

Because CT colonography is a new technology, it is not yet widely available or covered by health insurers. There is also need for a larger pool of physicians to perform CT colonography and interpret results of the test. Standardization test performance and results interpretation are necessary.

The AGA intends to help its members in practice and training understand the strengths and weaknesses of CT colonography and have the option to use this technology. This will necessitate a comprehensive approach to training and curriculum development, as well as the practical issues relevant to incorporating CT colonography into practice.

"Patients should not put off screening for colorectal cancer and polyps. Adults age 50 and older should talk with their physician about the screening tests currently available to them," says Dr. Keeffe.

Kimberly WIse | EurekAlert!
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