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A decision model and cost-effectiveness analysis of colorectal cancer screening and surveillance guidelines for average-risk adults |
Khandker R K, Dulski J D, Kilpatrick J B, Ellis R P, Mitchell J B, Baine W B |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The health interventions examined in the study were eight screening strategies for colorectal cancer: annual faecal occult blood test (FOBT), 3-year flexible sigmoidoscopy, 5-year flexible sigmoidoscopy, annual FOBT/3-year flexible sigmoidoscopy, annual FOBT/5-year flexible sigmoidoscopy, 5-year double-contrast barium enema (DCBE), 5-year colonoscopy (COL), and 10-year COL.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised average-risk persons aged 50 years and older without predisposing factors.
Setting The setting was community. The economic study was carried out in the USA.
Dates to which data relate Data on effectiveness were derived from studies published between 1982 and 1997. Resource use data were gathered between 1992 and 1994. The price year was 1994.
Source of effectiveness data Data on effectiveness and resource use were based on a review of the literature.
Modelling A dynamic state transition model was constructed to simulate disease process and to assess costs and survival of the eight screening procedures. Screening started at age 50 and continued until age 85. The eight primary health states were: disease-free, hyperplastic polyp, adenomatous polyp, undetected cancer, surveillance, treatment, death due to colorectal cancer or test complications and death from other causes. The complete model included more than 60 health states, depending on polyp histology (size and stage of development), location of polyp and cancer (distal or proximal), etc. The model also focused on assumptions regarding polyp dwell time and post-polypectomy surveillance.
Outcomes assessed in the review The outcomes derived from primary studies and used as model inputs were initial probabilities for adenomatous and hyperplastic polyps, incidence rates for new polyps, initial probabilities of various cancer stages, five-year survival rates, age-specific rates of death from other causes, and sensitivity and specificity of screening tests.
Study designs and other criteria for inclusion in the review Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included Seven primary studies were included in the review.
Methods of combining primary studies Primary studies were combined using narrative methods.
Investigation of differences between primary studies Results of the review The results of the review were as follows:
The initial probabilities for adenomatous and hyperplastic polyps were 25% (adenomatous) and 5% (hyperplastic).
The incidence rates for new polyps were 0.7% in the age group 50-65 years, 1% in the age group 66-70 years, and 1.5% in the age group 71-85 years.
The sensitivity of FOBT was 0.06 for small polyps, 0.10 for large polyps, and 0.60 for cancer.
The specificity of FOBT was 0.92.
The sensitivity of flexible sigmoidoscopy was 0.73 for small distal polyps, 0.97 for large distal polyps, and 0.97 for distal cancer.
The specificity of flexible sigmoidoscopy was 0.92.
The sensitivity of DCBE was 0.67 for distal polyps, 0.82 for large distal polyps, and 0.84 for distal cancer.
The specificity of DCBE was 0.75.
The sensitivity of COL was 0.79 for small distal polyps, 0.85 for large distal polyps, and 0.97 for distal cancer.
The specificity of COL was 1.
The values of other variables used in the decision model were not reported.
Methods used to derive estimates of effectiveness The compliance rate was derived using the authors' assumptions.
Estimates of effectiveness and key assumptions The authors assumed a compliance rate of 100% for the base-case analysis.
Measure of benefits used in the economic analysis Life-years saved with each intervention were used as benefit measure in the economic analysis and were derived using a decision model. A 3% discount rate was applied.
Direct costs A 3% discount rate was used as lifetime costs were estimated. Unit costs were reported only for screening procedures, while quantities of resources were not reported. The health service costs included in the economic evaluation were screening procedures, physician and hospital services, and treatment of complications. The cost/resource boundary appears to have been that of the third-party payer as Medicare costs were used. Outpatient costs were used in the analysis. Costs for elderly patients were derived from a 5% sample of all Medicare beneficiaries from 1992 through 1994, while costs for younger patients were derived from claims data for a large sample of privately insured patients. All costs were inflated to 1994 using the medical inflation rate of 4.8% in the USA.
Statistical analysis of costs Costs were treated deterministically.
Indirect Costs Indirect costs were not included in the analysis.
Sensitivity analysis Sensitivity analyses were performed to assess the robustness of the estimated cost-effectiveness ratios to variations in several model inputs, such as costs, compliance, transition probabilities, etc. In particular, the impact of variations in polyp dwell time was investigated and two alternative scenarios were investigated at the end of the tenth year with a polyp: in one scenario, pre-cancerous polyp turned to cancer with a probability of 1.0 and in another scenario with a probability of 0.25.
Estimated benefits used in the economic analysis Life-years gained were:
18.14 with no screening;
18.24 with annual FOBT;
18.23 with 3-year flexible sigmoidoscopy;
18.23 with 5-year flexible sigmoidoscopy;
18.25 with annual FOBT/3-year flexible sigmoidoscopy;
18.25 with annual FOBT/5-year flexible sigmoidoscopy;
18.25 with 5-year DCBE;
18.25 with 5-year COL; and
18.25 with 10-year COL.
Cost results Total per patient cost:
$643 with no screening;
$2,058 with annual FOBT;
$2,079 with 3-year flexible sigmoidoscopy;
$1,713 with 5-year flexible sigmoidoscopy;
$2,854 with annual FOBT/3-year flexible sigmoidoscopy;
$2,639 with annual FOBT/5-year flexible sigmoidoscopy;
$2,577 with 5-year DCBE;
$3,906 with 5-year COL; and
$2,602 with 10-year COL.
Synthesis of costs and benefits An incremental analysis was performed to combine costs and benefits of the screening procedures in comparison with no screening.
The extra cost per life-year gained:
$14,394 with annual FOBT;
$16,261 with 3-year flexible sigmoidoscopy;
$12,636 with 5-year flexible sigmoidoscopy;
$20,334 with annual FOBT/3-year flexible sigmoidoscopy;
$18,204 with annual FOBT/5-year flexible sigmoidoscopy;
$17,553 with 5-year DCBE;
$28,724 with 5-year COL; and
$17,696 with 10-year COL.
The estimated cost-effectiveness ratios were very sensitive to the assumptions regarding polyp dwell time. At low compliance levels, FOBT reduced its cost-effectiveness. Variations in other model inputs were generally of less importance.
Authors' conclusions The authors concluded that sigmoidoscopy every 5 years and annual FOBT were the most cost-effective screening procedures for colorectal cancer. However, at low compliance rates, the cost-effectiveness of annual FOBT diminished.
CRD COMMENTARY - Selection of comparators The rationale for the choice of the comparators was clear, as all eight screening strategies were included in the AGA guidelines. No screening was then selected as the basic comparator. You, as a user of this database, should decide whether they represent widely used screening procedures in your own setting.
Validity of estimate of measure of effectiveness The analysis of the effectiveness was based on data derived from several published studies, but no formal review of the literature was undertaken. Primary studies were combined using narrative methods and the authors did not state whether they took into account differences between primary studies when estimating effectiveness. Several sensitivity analyses were performed to investigate the uncertainty around the model inputs.
Validity of estimate of measure of benefit The benefit measure used in the analysis was life-years saved, which represents a widely used benefit measure for screening programmes, thus the comparability of the benefits of colorectal cancer screening with other screening procedures was ensured. Appropriate discounting of benefits was performed.
Validity of estimate of costs The analysis of costs appears to have been conducted from the perspective of the third-party payer and it appears that all relevant categories of costs were included in the study. The price year was reported, thus facilitating reflation exercises in other settings. However, a detailed breakdown of costs was not provided and unit costs were reported only for screening procedures. Costs were treated deterministically in the base case, but several sensitivity analyses were performed. Outpatient costs were used to determine the costs of the interventions.
Other issues The authors made some comparisons of their findings with those from other studies. As regards the issue of the generalisability of the study findings to other settings, the authors commented that the study was oriented towards the USA, thus caution should be required when extrapolating the results to other countries. In addition, several sensitivity analyses were conducted, thus enhancing the external validity of the analysis. The study referred to the general population of average-risk colorectal cancer patients and this was reflected in the conclusions of the study. Although the comparator was stated to be no screening and, as such, all incremental analyses were conducted along these lines, incremental analyses between the different screening strategies may have been very useful for policy makers.
Implications of the study The author's note that a successful screening policy depends on societal resource constrains and value judgements. It was also suggested that future studies should focus on patient quality of life and societal impacts related with colorectal cancer and screening procedures.
Source of funding Conducted under Contract No 282-95-2002 from the former Agency for Health Care Policy and Research.
Bibliographic details Khandker R K, Dulski J D, Kilpatrick J B, Ellis R P, Mitchell J B, Baine W B. A decision model and cost-effectiveness analysis of colorectal cancer screening and surveillance guidelines for average-risk adults. International Journal of Technology Assessment in Health Care 2000; 16(3): 799-810 Other publications of related interest Letter to the editor. International Journal of Technology Assessment in Health Care 2001;17(3):451-454.
Indexing Status Subject indexing assigned by NLM MeSH Aged; Aged, 80 and over; Colorectal Neoplasms /diagnosis /economics; Cost-Benefit Analysis; Decision Trees; Disease Progression; Female; Humans; Male; Mass Screening /economics /methods; Middle Aged; Population Surveillance; Practice Guidelines as Topic; Risk Factors AccessionNumber 22000008312 Date bibliographic record published 31/05/2003 Date abstract record published 31/05/2003 |
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