Economic Models of Colorectal Cancer Screening in Average-Risk Adults Workshop Summary (2005) / Chapter Skim
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Workshop Summary
Workshop Summary
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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.
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THE COLLABORATIVE MODELING EXERCISE Origin of the Exercise The idea for collaboration among research teams that maintain published models of CRC screening grew out of a recent review by Michael Pignone and colleagues for the U.S. Preventive Health Services Task Force (Pignone et al., 2002)
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The five selected strategies were: 1) F/S: Annual fecal occult blood testing in combination with a flexible sigmoidoscopy every five years; 2)
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TABLE 1. Standardized Assumptions for Pre-workshop Collaborative Exercise COSTS Fecal occult blood est $10 Colonoscopy-diagnostic $625 Colonoscopy with polypectomy $900 Pathology per polyp $65 Sigmoidoscopy-screening $200 Sigmoidoscopy with polypectomy N/A Sigmoidoscopy with biopsy $375 Prototype tadiology procedure $200 Lifetime CRC treatment cost Local $24,000 Regional $31,000 Distant $40,000 Cost of treating perforation $24,000
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Colonooscopy mortality 0.01percent rate Sigmoidoscopy major 0 percent complication Sigmoidoscopy mortality 0 percent rate Prototype radiology 0 percent FOLLOW-UP Fecal occult blood test Assume all positive fecal occult blood tests are followed by colonoscopy with polypectomy if true positive, or diagnostic colonoscopy if false positive Sigmoidoscopy a) Assume all positive screens are fol lowed by colonoscopy with polypectomy if true positive, or diagnostic colonoscopy if false positive b)
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Although an abundance of evidence suggests compliance is far less than perfect, it would have been time-consuming or impossible for all of the research teams to reconfigure their models to accommodate more realistic assumptions. This somewhat opportunistic standardization process underscores the danger of interpreting the standardized results as endorsing any specific colorectal cancer screening strategy, especially because the effectiveness of some strategies is bound to be more heavily dependent on high rates of compliance than others.
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continued c odeledm cent Vijan No 0.05 0.05 0.05 0.3 0.5 Not 9750.
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continued Vijan Yes 850.
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p TIONSP remp com CRC-local CRC- CRC-distant cost) polyp cost cost cost)
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with patient ancelipm liance? pm with CSCPY CSCPY U to tionsp ci co BTOF IGSF technolo ior F/a oach istantd NCE assum cost cost liancepm patient liancepm alu co pr on liancepm with with with with as or appr eening All co of co co scr bei ES: levant-er sex-specif Initial Continuing Final individ TABLE COMPLIA Does pety patient's liancepm liancepm liancepm liancepm liancepm Does for Is pendent Does with Co Co Co Co veillance Descr co NOT not.a age-and
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Those results would allow an indirect comparison of natural history assumptions across the models.3 Specification of Model Outputs For every model run, the research teams provided the coordinators of the exercise4 with estimates of the total number of years of life lived and total medical costs incurred by a population of 100,000 average-risk 50-year-old adults from age 50 until death or age 85, whichever comes first.5 These outputs were reported both as simple totals and in terms of their net present value (NPV) at the starting age (age 50)
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The research teams estimated the number of years of life lived (life expectancy) by an average 50-year-old and lifetime CRC-related costs per person, when no screening program was in effect and all assumptions were set to each team's original values (Table 5)
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Some participants posited that differences in assumptions about cancer incidence probably account for the remaining variation in colorectal cancer costs. Screening Estimates Under Original Assumptions Differences among the five models in estimates of the effect of screening under each team's original assumptions were presented by Michael Pignone and discussed by the research teams and other participants.
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14 ECONOMIC MODELS OF COLORECTAL CANCER SCREENING A Years of Life Gained 6,000 5,000 Harvard 100K 4,000 per Ladabaum 3,000 Miscan gained earsY 2,000 Vanderbilt Vijan NPV 1,000 0 F/S S R C F Screening Strategy B Lifetime Cost 1,600 1,400 Harvard 1,200 Ladabaum capita 1,000 per Miscan 800 Cost Vanderbilt 600 NPV 400 Vijan 200 0 F/S S R C F Screening Strategy FIGURE 1. Years of life gained and liftetime costs of screening: original assumptions.
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So, participants reviewed the performance of strategies with each other as reported by the research teams. The first step in making such comparisons is to rule out any screening strategy that is both less effective and more costly than at least one other.
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. Thus, according to Pignone, under their original assumptions, the five research teams would present very different options to policy makers.
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30,000 25,000 Harvard gained e 20,000 lif Ladabaum of 15,000 Miscan eary Vanderbilt per 10,000 Vijan Cost 5,000 0 F/S S R C F Screening Strategy FIGURE 4. Cost-effectiveness of screening: standardized assumptions.
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The range of estimates for lifetime costs associated with a particular strategy declined substantially for two strategies but increased slightly for two others.10 TABLE 8. Effect of Standardizing Individual Assumption Groups on Variation Across Models: Ratio of Highest Estimate to Lowest Estimate F/S S C F Net Present Value of Years of Life Gained Due to Screening Original assumptions 1.3 1.6 2.4 1.7 Costs std 1.3 1.6 2.4 1.7 Test performance std 1.2 1.8 1.4 1.4 FU/Surveillance std 1.3 1.7 1.5 1.7 Compliance std 1.4 1.8 1.3 1.3 All groups std 1.4 2.0 1.4 1.5 Net Present Value of Lifetime Costs Incurred Due to Screening Original assumptions 3.9 5.2 3.6 2.9 Costs std 2.8 3.2 4.1 NA Test performance std 4.7 7.8 3.8 6.0 FU/Surveillance std 4.0 5.0 4.2 2.5 Compliance std 3.0 3.9 2.5 5.6 All standard 1.9 2.0 1.5 2.0 NOTES: Net present value computed at 3 percent per annum; FU/Surveillance = Follow up and Surveillance; std = standardized; NA = Not available.
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, some screening technologies may detect them with higher frequency than others. In particular, endoscopy and radiology would be more likely to detect non-adenomatous polyps than would fecal occult blood testing, because non-adenomatous polyps rarely bleed.11 Once detected, however, such lesions are typically removed and sent for biopsy because they cannot be differentiated from adenomas by any other method.
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The Vanderbilt team was the first to recognize the impact of non-adenomas on the standardized results of the pre-workshop exercise. Vanderbilt's estimates of the lifetime costs of all screening strategies were much higher than those reported to the workshop by the other research teams (see Figure 3B)
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(new) F/S $99,977 $79,920 $55,878 $56,969 $355,647 $355,608 S SD SD SD SD SD SD R WD SD WD SD $209,906 $114,510 C SD SD SD SD WD SD F $11,632 $7,272 $5,980 $9,676 $10,073 $8,659 NOTES: F/S = annual fecal occult blood test, sigmoidoscopy every 5 years; S = sigmoidoscopy every 5 years; R = prototype radiology procedure every 5 years; C = colonoscopy every 10 years; F = annual fecal occult blood test; WD = strategy is weakly dominated by at least one other strategy; and SD = strategy is strongly dominated by at least one other strategy.
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Researchers have posited that some adenomas may never bleed, while others may bleed regularly. If more were known about whether such patterns actually exist, and the frequency with which they do, models could be constructed that would adjust the assumed probability that people with adenomas receive positive fecal occult blood testing results in the second and subsequent years of a screening program, based on their test results in previous years.
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Brian Mulhall's review of the wide range of estimates of fecal occult blood test sensitivity and specificity for adenomas in people who are recommended for screening suggested that uncertainty about test performance is not limited to new, emerging, or uncommon technologies. Fecal occult blood testing, one of the oldest technologies available for CRC screening, has been the focus of several large-scale randomized screening trials, all of which have demonstrated that it can reduce mortality from CRC (Jorgensen et al., 2002; Mandel et al., 1999; Scholefield et al., 2002)
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Uncertainty about compliance is also high because surveys define compliance differently. Sally Vernon observed that surveys that measure the number of patients who receive fecal occult blood test kits from their physicians typically report high compliance, whereas those that measure the number of test kits returned for analysis show much lower rates.
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The presentations by leaders of the five research teams showed that several have used data from large fecal occult blood testing screening trials to evaluate the extent to which their models' predictions of cancer incidence and mortality over time agree with the results found in the trials. The ongoing PLCO trial (Schoen et al., 2003; Gohagan et al., 1995)
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Wagner also observed that published CEAs of CRC screening have often evaluated a single screening strategy not examined in published work by other modeling teams. That practice makes it difficult for readers to assess the level of agreement across models.
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Sandeep Vijan observed that assuming low compliance for certain screening or surveillance procedures is one way models could implicitly account for such constraints. Seth Glick emphasized the divergence between test performance under ideal quality assurance programs and test performance in current practice.
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When the high lifetime costs of some very effective screening strategies become apparent in all models, a natural next step is to explore how those costs could be reduced, without compromising effectiveness, by fine-tuning strategies. Such fine-tuning drives modelers to add more branches to their strategies, which places even greater demands on the clinical and epidemiological evidence available to support such modeling.
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Virtually all economic models, drawing from a wealth of clinical trials and epidemiological studies, have found that colorectal cancer screening decreases mortality from the disease. The message to physicians, payers, and patients that periodic screening for colorectal cancer is an effective preventive measure continues to have urgency.
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Many participants commented on the value of the conversation for further refinement of their models (in the case of the research teams) and for research ideas (in the case of clinical and epidemiological researchers)
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