Colorectal cancer is one of the major causes of death worldwide. Computed tomography (CT) colonography is a relatively new, effective screening tool for this type of cancer. Existing evidence indicates that CT colonography is not as cost-effective as colonoscopy in colorectal cancer screening, but it can be an alternative, cost-effective method in cases where colonoscopy is not available or not acceptable.
by Dr I Mavranezouli
Colorectal cancer is a leading cause of death worldwide. Most often it develops from benign adenomas evolving over time. Early detection can lead to effective treatment, thus significantly reducing mortality. Several screening tools are available for this purpose, and many government agencies have implemented screening policies aiming at early diagnosis and treatment of this type of cancer. Among these, computed tomography (CT) colonography has recently emerged as an accurate method for detection of advanced neoplasia. CT colonography has the advantage of being minimally invasive compared with colonoscopy. But in the area of healthcare, where costs are constantly rising and budgets are constrained, the question is however the following: is CT colonography a cost-effective option in colorectal cancer screening? In other words, is it worth the money?
Economic evaluation of healthcare technologies
The aim of economic evaluation in healthcare is to maximise the health of the population by ensuring the most efficient use of scarce resources. This is achieved by comparing alternative courses of action in terms of both their costs and consequences [1]. One of the most common types of economic evaluation is cost-effectiveness analysis, in which consequences are represented by a single health outcome measure expressed in physical units (e.g. number of life years saved, LYS).
The cost-effectiveness of a healthcare intervention is determined by comparing it to an appropriate alternative, normally routine care or other relevant interventions available in clinical practice. When one intervention is less costly and more effective than the intervention to which it is compared, then it is clearly cost-effective and is called “dominant”. The opposite conclusion is reached when the intervention is less effective and more expensive than that to which it is compared. If one intervention is both costlier and more effective, then incremental analysis is required. The incremental cost-effectiveness ratio (ICER) is calculated as the difference in costs divided by the difference in effectiveness between two interventions; the decision-maker needs to assess whether the extra health benefit is worth the extra cost after determining the maximum cost (threshold) s/he is willing to pay per unit of effectiveness. An ICER below, or equalling the threshold indicates a cost-effective intervention. Finally, in a situation where the new intervention provides less benefit than the intervention to which it is compared but at a lower cost, the decision-maker needs to judge whether the magnitude of cost-saving justifies the reduction in benefit, by comparing the estimated ICER with the set cost-effectiveness threshold.
Cost-effectiveness of CT colonography
Several papers have assessed the cost-effectiveness of CT colonography as a screening tool for colorectal cancer in the US [2-8], Canada [9], Denmark [10] and Italy [11]. The vast majority have employed decision-analytic modelling techniques to assess the long term costs and benefits (including cost-savings) of CT colonography compared with other screening methods and/or no screening. Such modelling techniques enable synthesis of cost and clinical data from various sources and allow assessment of the cost-effectiveness of healthcare strategies in the long term.
Using a cost-effectiveness threshold of $50,000/LYS, which is a broadly accepted threshold in the US [11], CT colonography has been reported to be more cost-effective than no screening [2-7,11], flexible sigmoidoscopy (FS) [4,5,11], faecal occult blood testing (FOBT) [4] and a combination of FOBT/FS [4]. However, the appropriate intervention to which CT colonography should be compared is colonoscopy, since this is one of the most accurate and widely implemented methods for the detection of colorectal cancer (reflecting routine care in many settings).
Conclusions on the relative cost-effectiveness between CT colonography and colonoscopy are controversial: five out of the 10 economic analyses have concluded that CT colonography is not cost-effective relative to colonoscopy [2-4,8,9]. Of these, three reported that colonoscopy was dominant over CT colonography [3,8,9] and two showed that colonoscopy was costlier than CT colonography but with an ICER lower than $11,000/LYS [2,4], which is below the $50,000/LYS threshold accepted in the US. Another study stated that CT colonography might be cost-effective at some institutions which had the appropriate hardware and organisation [10].
The four studies concluding that CT colonography is more cost-effective than colonoscopy have been conducted by the same research team and have used the same decision-analytic model structure [5-7,11]. In one study colonoscopy was found to be costlier overall than CT colonography in Italy, with an ICER reaching €15,000/LYS. Judging that the ICER was high, the authors concluded that colonoscopy was not cost-effective compared with CT colonography [11]. However, such an ICER would have been considered favourable for colonoscopy in the US and other settings. In fact the same research team set a cost-effectiveness threshold of $100,000/LYS in two of their other publications [6-7]. Three further publications from the team compared colonoscopy with CT colonography. In the first, diminutive polyps were ignored (i.e. not referred for colonoscopy and subsequent polypectomy) [5]. The second study considered the ability of CT colonography to detct extracolonic cancer and abdominal aortic aneurysms (AAA) [6]. The third considered CT colonography combined with computer-aided detection (CAD) performed by experienced readers [7]. In all these studies the authors concluded that CT colonography was more cost-effective than colonoscopy [5-7]; moreover, when the ability to detect extracolonic cancer and AAA was considered, CT colonography was dominant over colonoscopy even when the latter was combined with abdominal ultrasonography [6].
From the cost and effectiveness data reported in the above papers [5-7] it was possible to estimate the ICER of colonoscopy versus CT colonography when:
a. all polyps detected by CT colonography were reported regardless of their size [5]
b. costs and benefits associated with detection of extracolonic cancer or AAA were ignored [6] and
c. CT colonography without CAD was performed by experienced readers [7].
The respective estimated ICERs were $42,000/LYS, $51,000/LYS and $182,000/LYS. With the exception of the first figure (which is nevertheless still very high compared to other published findings), the other two figures indicate that colonoscopy is not cost-effective compared to CT colonography when a cost-effectiveness threshold of $50,000/LYS is used. This is true even when the ability of CT colonography to detect extracolonic cancer or AAA is ignored, or when CT colonography is not accompanied by CAD (but is performed by experienced readers). Such conclusions are inconsistent with previous findings [2-4,8,9]; this discrepancy in results across studies can be explained by the use of different model input data and assumptions. It should be noted that two of the studies demonstrating that colonoscopy dominates CT colonography had also assumed that polyps <6mm found by CT colonography were ignored [8,9].
Factors affecting the relative cost-effectiveness of CT colonography
A recent critical review of the economic literature identified several factors potentially affecting the cost-effectiveness of CT colonography [13].
CT colonography performance: sensitivity analysis performed in the modelling studies showed that variations in this factor had little impact on the results. The experience of readers obviously affects the test characteristics of CT colonography; evidence suggests that it also improves its cost-effectiveness, but this issue needs to be explored further.
Colonoscopy performance and complications: published economic studies have not considered the experience/performance of the endoscopist as a baseline factor affecting the relative cost-effectiveness between CT colonography and colonoscopy, although polyp detection rates can vary considerably across colonoscopy centres. On the other hand, the rate of colonoscopy complications (e.g. perforation) is unlikely to have a strong negative impact on its cost-effectiveness relative to CT colonography, provided that colonoscopy is undertaken by trained endoscopists.
Intervention costs: these have been shown to significantly affect the relative cost-effectiveness of CT colonography and colonoscopy. Therefore, conclusions may differ in healthcare settings where the cost ratio between the two inter-ventions varies considerably from that utilised in modelling studies.
Compliance: different levels of compliance between CT colonography and colonoscopy significantly affect their relative cost-effectiveness. Existing models have assumed the same baseline levels of compliance for the two interventions; further research is needed to investigate the relative acceptability of these two screening methods in order to determine their relative cost-effectiveness more accurately.
Extracolonic findings: although published evidence suggests that the cost-effectiveness of CT colonography is higher when its ability to detect extracolonic cancer and abdominal aortic aneurysms is considered, these findings are controversial and need to be confirmed by further research.
Non-reporting of diminutive polyps: here, the evidence is also controversial. Although it has been reported that ignoring diminutive polyps makes CT colonoscopy cost-effective relative to colonoscopy, this is not confirmed by other literature. On the contrary, there is conflicting evidence that colonoscopy dominates CT colonography even when diminutive polyps detected by the latter technique are ignored.
Conclusion
Existing evidence on the cost-effectiveness of CT colonography is rather controversial. Critical appraisal of the literature suggests that CT colonography is rather unlikely to be a cost-effective alternative to colonoscopy, even when small polyps are not referred for further investigation. However, when colonoscopy is not available or not acceptable, CT colonography can be recommended as an alternative, cost-effective method for colorectal cancer screening. These conclusions, which are in line with recent guidelines on colorectal cancer screening published by the American College of Gastroenterology [14], need to be established by future research. It must be noted that the cost-effectiveness of CT colonography depends largely on its cost relative to colonoscopy. Therefore, it is possible that CT colonography could be potentially more cost-effective than colonoscopy in some healthcare settings.
References
1. Drummond MF, Sculpher MJ, Torrance GW, O’Brien BJ, Stoddard GL. Methods for the economic evaluation of health care programmes. 3rd ed. Oxford: Oxford University Press, 2005.
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6. Hassan C, Pickhardt PJ, Laghi A, Kim DH, Zullo A, Iafrate F, Di Giulio L, Morini S. Computed tomographic colonography to screen for colorectal cancer, extracolonic cancer, and aortic aneurysm: model simulation with cost-effectiveness analysis. Arch Intern Med 2008;168(7):696-705.
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11. Hassan C, Zullo A, Laghi A, Reitano I, Taggi F, Cerro P, Iafrate F, Giustini M,Winn S, Morini S. Colon cancer prevention in Italy: cost-effectiveness analysis with CT colonography and endoscopy. Dig Liver Dis 2007;39(3):242-250.
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13. Mavranezouli I, East JE, Taylor SA. CT colonography and cost-effectiveness. Eur Radiol 2008;18(11):2485-2497.
14. Rex DK, Johnson DA, Anderson JC, Schoenfeld PS, Burke CA, Inadomi JM. American College of Gastroenterology Guidelines for Colorectal Cancer Screening 2008. Am J Gastroenterol 2009; doi: 10.1038/ajg.2009.104
The author
Ifigeneia Mavranezouli, MD, MSc
Senior Health Economist
National Collaborating Centre for Mental Health
BPS-CORE
Research Department of Clinical, Educational & Health Psychology
UCL, Philips House,
1-19 Torrington Place
London WC1E 7HB
UK
Tel +44 207 679 1964
e-mail: i.mavranezouli@ucl.ac.uk
