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Institute of Medicine (US); National Research Council (US); Pignone M, Russell L, Wagner J, editors. Economic Models of Colorectal Cancer Screening in Average-Risk Adults: Workshop Summary. Washington (DC): National Academies Press (US); 2005.

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Economic Models of Colorectal Cancer Screening in Average-Risk Adults: Workshop Summary.

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Colorectal cancer (CRC) is the second leading cause of death from cancer in the United States (Edwards et al., 2002). Research has shown that screening adults for early cancers or their precursor lesions, followed by appropriate therapy and continued surveillance, can reduce CRC incidence and mortality (Curry, 2003). A general consensus has emerged that periodic screening of adults over age 50 is a valuable preventive intervention and today most health plans cover CRC screening (United States General Accounting Office, 2004). Yet, there is continued uncertainty about the specific screening strategies that should be offered to individuals who are at average risk for CRC.

There are two reasons for the prevailing uncertainty about what screening strategies make sense for these average-risk adults. First, the number of potential screening strategies is large, encompassing not only the choice of technology (or technologies) but also decisions about the age at which screening should begin, the frequency with which it should occur, and the age at which routine screening should end. Several medical technologies are available to detect early cancers or benign adenomas, the polyps that precede most colorectal cancers. Those technologies vary widely both in cost and detection capabilities. The list includes flexible sigmoidoscopy, colonoscopy, barium enema x-ray, and fecal occult blood tests. The choices are growing, too. New technologies, including imaging and molecular markers, are currently under development. Their entry will expand the range of alternative screening strategies even further.

A second factor that makes it difficult to settle on a specific strategy is that much is unknown about the natural history of colorectal cancer—how fast or slowly it develops, how frequently it arises from pre-existing benign adenomas, and how long those adenomas remain in a benign but detectable state before they convert to cancer. Although new information about these questions has emerged in recent years, it is indirect because, once they are detected, cancers or adenomas are virtually never left behind to grow and be observed. The effectiveness and cost of any screening strategy depend on the details of natural history and as long as those details remain unknown, it is impossible to be sure that one strategy is unequivocally better than another in the absence of a head-to-head trial comparing different strategies. Such a trial is unlikely to be performed because the cost and duration would be prohibitive.

Economic models of CRC screening offer a means for addressing questions about how to screen for CRC. Beginning with the work of David Eddy in the late 1970s (Eddy, 1980), many academic and government researchers have built computer models to describe the natural history of CRC and analyze the costs and effects of altering that history with selected screening strategies (Eddy et al., 1987; Frazier et al., 2000; Glick et al., 1998; Joseph et al., 1988; Khandker et al., 2000; Ladabaum et al., 2004b; Lieberman, 1995; Loeve et al., 1999, 2000; Neilson and Whynes, 1995; Ness et al., 2000; Sonnenberg and Delco, 2002; Sonnenberg et al., 2000; Vijan et al., 2001; Wagner et al., 1991, 1996; Whynes, 2004). The purpose of such models is to help decision makers evaluate which strategies to pay for, recommend, adopt, or use. As the field of cost-effectiveness analysis (CEA) in medicine advances (Gold et al., 1996), and as new evidence on the natural history of CRC emerges, the models have improved. But they have not been able to resolve the uncertainty about the comparative performance of different CRC screening strategies. Rather, they continue to disagree about how alternative strategies stack up against one another in their health effects and costs (Curry, 2003; Pignone et al., 2002).

Public health policy makers increasingly rely on CEAs to help them sift through the many choices confronting them. When different CEA models give different answers to the same question, confidence in their usefulness may suffer, since it is unclear to what extent the disagreement arises from uncertainty about the underlying evidence, which affects all decision making approaches, or from the modeling methods used by different modelers. Understanding the reasons for differences among models is therefore an important first step in building the public's confidence that CEA can provide objective and informative insights into the consequences of health policy choices.

The Institute of Medicine's (IOM's) National Cancer Policy Board (NCPB) convened the workshop, “Economic Models of Colorectal Cancer Screening in Average-Risk Adults” on January 26-27, 2004, to explore the reasons for differences among leading CEA models of CRC screening. Participants discussed the results of a collaborative pre-workshop exercise undertaken by five research teams that have developed and maintained comprehensive models of CRC screening in average-risk adults. The purpose of the exercise was to provide workshop participants with insights into each model's structure and assumptions and possible explanations for differences in their published analyses. Workshop participants also examined the current state of knowledge on key inputs to the models with a view toward identifying areas where further research may be warranted.

In keeping with the purpose of IOM workshops, this summary of its proceedings presents the individual perspectives and research of people who made presentations at the workshop and of many other experts who participated. This summary does not contain consensus recommendations, nor does it represent a consensus opinion of the IOM's NCPB. Nor is it intended as a guide for conducting or using cost-effectiveness analyses in CRC screening decisions.

It is particularly important to recognize that the purpose of the workshop was not to consider the relative merits of different strategies for CRC screening, or to suggest which CRC screening strategy is best. It was solely to consider the commonalities and differences among the CEA models bearing on the subject. The demand for more certain guidance from models by those who recommend or pay for screening strategies, while clearly a motivating force behind the workshop, was not its focus. More certain guidance may result in the future as modelers continue to grapple with and explain the differences in their findings.

Copyright © 2005, National Academy of Sciences.
Bookshelf ID: NBK83879


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