Spring 2006 - Vol.1, No.1

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COLORECTAL CANCER SCREENING:

BRUCE H. POKORNEY, M.D.

Chief Medical Officer, Sr. VP, Medical Affairs,

Lancaster General Hospital

Gastroenterologist

EDGAR C. FEARNOW, III, M.D.

Chief, Division of Computerized Tomography,

Lancaster General Hospital

ABSTRACT

Colorectal cancer continues to be one of the leading causes of death in the United States. Despite the potential of screening methods to decrease mortality, screening rates among eligible individuals are abysmal. Conventional colonoscopy remains the gold standard for colorectal cancer screening, but poor patient compliance and negative attitudes toward this procedure may contribute to the low screening rates. CT colonography is more patient-friendly and may increase screening rates for colorectal cancer. Based on initial studies, it holds promise as a screening method, and may ultimately decrease mortality rates from colon cancer. However, CT colonography technique and technology must improve before the procedure can be widely adopted for screening. LGH physicians find that CT colonography is a helpful tool when optical colonoscopy is not feasible or successful, but should not be used for widespread screening of average risk individuals until further validation studies are completed.

DISCUSSION

Colorectal cancer remains the second most common cause of cancer death in the US, afflicting more than 145,000 people and killing more than 56,000 people each year. These bleak statistics persist despite reductions in the mortality rate during the last decade. Fortunately, screening methods can profoundly affect morbidity and mortality rates from colorectal cancer because it is a highly preventable and curable disease. The natural history of the disease, in which pre-malignant adenomatous polyps can take up to 10 years to develop into malignant ones, presents an ideal scenario for preventive screening to be effective by allowing identification and removal of pre-malignant polyps before cancer occurs.

For individuals with no other risk factors, who have an average cumulative risk of developing colorectal cancer of 6 percent, as well as for individuals with increased risk, conventional optical colonoscopy is still widely accepted as the best screening method. Despite the potential effectiveness of screening in reducing mortality, less than one-fourth of the eligible population in the US undergoes colorectal screening by any method. The low screening rate is the result of poor patient compliance, negative patient and physician attitudes toward screening, and, in particular, toward colonoscopy, and lack of trained colonoscopists to meet demand in some regions of the US. Optical colonoscopy, still considered the gold standard for screening because of its high sensitivity and specificity, has the distinct advantage of being the only screening method that can be used as both a diagnostic and a therapeutic tool. Nonetheless, optical colonoscopy is far from being the perfect screening method—it is expensive, invasive, resource-intensive, and has a small, but significant risk of complications. Many patients find that the bowel preparation required for the test is very uncomfortable. In addition, optical colonoscopy has limitations in that abnormalities, including small polyps or early cancers, may be missed at the hepatic and splenic flexures or in the cecum, where up to 20 percent and 15 percent of colorectal cancer occur, respectively.

Despite its limitations and disadvantages, initial colonoscopy for colorectal cancer screening has a higher benefit-cost ratio than any other screening test currently recommended for any disease. The technology used continues to advance, and developments, such as chromoendoscopy and fully digital high-resolution imaging, will eventually further improve its sensitivity and specificity.

Only radiologists with a tremendous amount of experience - not only in general CT, but with the three-dimensional endoluminal view of the colon in particular, should be performing and reading CT colonography. Fortunately, radiologists at LGH have considerable experience with CT colonography. For optimum readability and patient comfort, thinner multi-slice CT scanners and three-dimensional software analysis packages are essential. At LGH, radiologists primarily perform examinations using a 16-slice scanner, and review examinations in both two-dimensional multiplanar and three-dimensional endoluminal modes.

How would the widespread use of CT colonography affect the guidelines for patient care based on the size of polyps found on examination? Currently, the size and number of polyps found at initial screening is a significant factor in determining the next steps. Polyp size is often divided into three categories: 1 cm or larger, 6 to 9 mm, and 5 mm or smaller. For optical colonoscopy, all identified polyps, regardless of size, are immediately removed during the procedure. For CT colonography, patients would require immediate therapeutic colonoscopy for polyps 1 cm or larger. Many practitioners agree that polyps 5 mm or smaller are insignificant, and, if found by CT colonography, may be followed over time. The problem arises with polyps between 6 and 9 mm, a range in which the sensitivity and specificity of CT colonography can be more unpredictable and reader dependent.

Most physicians, including those radiologists and gastroenterologists who have developed the joint CT colonography guidelines at LGH, concur that 6 to 9 mm polyps found at CT colonography warrant colonoscopic removal. The situation becomes further complicated by the fact that differentiating between a 6 mm and 5 mm polyp using either optical colonoscopy or CT colonography is often difficult. Measurements within 1 mm are clearly subject to considerable operator or reader variability.

The close collaboration of gastroenterologists and radiologists at LGH provides an important model for interspecialty cooperation. The Department of Radiology and the Division of Gastroenterology worked collaboratively to define the current best uses for CT colonography from the patient’s perspective. Currently, a gastroenterologist must order the CT colonography, and the Department of Radiology can usually carry out the study on the same day a conventional colonoscopy has been attempted. Since the patient has already undergone colon preparation, a same day study is a great convenience for the patient. In the future, as the use of CT colonography increases, we hope that the reciprocal arrangement will also be feasible: if the findings of CT colonography require a followup colonoscopy for polyp removal, the Division of Gastroenterology will be able to accommodate patients on the same day they undergo primary CT colonography screening.

As the technology evolves even further, close collaboration between radiologists and gastroenterologists such as we have developed at LGH is essential to integrate CT colonography into the care plan for patients. Ultimately, the collaboration between both specialties has flourished because of the effort to place what is best for the patient as the highest priority, not what is best for the providers’ work processes or specialty.

The future of CT colonography in colorectal cancer screening remains dynamic. Software analysis packages continue to improve, shortening the procedure time for patients. Researchers have studied CT colonography using ultra-low dose radiation and found that a high sensitivity was maintained while the exposure to radiation was greatly reduced. Fecal tagging using iodinated contrast material may eventually eliminate the need for bowel preparation and greatly increase patient compliance.