The Role of CT Colonography in a Colorectal Cancer Screening Program

Computed tomography colonography (CTC) has the potential to become a major component of colorectal cancer (CRC) screening programs and to have a significant effect on CRC prevention. This article describes the potential role of CTC within the framework of colorectal cancer screening. Current screening recommendations and traditional screening tests are reviewed, followed by a summary of recent study results on the use of CTC as a screening tool. Several factors that are affecting the acceptance and adoption of CTC are outlined. Although CTC is valuable and holds considerable promise as a way to increase the use of CRC screening, these issues need to be addressed before CTC becomes more widely disseminated as a screening modality.

Colorectal cancer (CRC) remains the third most commonly diagnosed cancer and the second leading cause of cancer death in the United States. In 2009, an estimated 146,970 new cases of CRC were diagnosed, and approximately 49,920 people died of the disease. The average lifetime risk of developing CRC is 6%, with men and women almost equally affected. CRCs typically develop from adenomatous polyps which progress from small to large (>1 cm) size, and then to high-grade dysplasia and cancer. This progression from adenoma to carcinoma is believed to take at least 10 years. The slow transition from polyps to CRC in most patients allows opportunities to prevent cancer by removing polyps, and to prevent cancer death by finding and removing early cancers. Several screening tests are available and well established, each with advantages and limitations. Although stool-based tests improve disease prognosis mainly by detecting early stage cancers, endoscopic and radiologic tests that visualize the bowel mucosa have the potential to also prevent cancer by detecting polyps that can be removed before malignant transformation. This article discusses the potential role of computed tomographic colonography (CTC) in a CRC screening program by first providing a brief review of current screening recommendations and traditional screening options, followed by a discussion of specific CTC test characteristics, economics and implementation issues that may affect the adoption and positioning of CTC within the overall framework of CRC screening.

CRC screening: prevalence and barriers

Despite considerable evidence supporting the effectiveness of CRC screening and the availability of various screening tests, half of the US population aged 50 years and older is still not undergoing CRC screening according to 2005 estimates from the National Health Interview Survey. This compares with more than 80% of eligible women participating in breast cancer screening programs. The prevalence rates for CRC screening are lower among people aged 50 to 64 years and especially low among individuals who are nonwhite, have fewer years of education, lack health insurance coverage, and are recent immigrants. These low rates cannot be attributed to any single factor (such as fear of undergoing colonoscopy) but are related to a variety of issues including lack of public knowledge about the importance of screening and testing options, lack of time, fear of being diagnosed with cancer, embarrassment, unpleasantness of the test, as well as concerns about costs. Health insurance barriers such as insurance status and coverage limitations are also significant factors. Although the addition of new and potentially less invasive screening tests such as CTC may overcome some of these barriers, they are unlikely to resolve all of them. Their effect on overall screening rates and the costs of screening can therefore not be easily predicted and need to be carefully studied and evaluated over time.

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