Imatinib for the treatment of patients with unresectable and/or metastatic gastrointestinal stromal tumours: systematic review and economic evaluation

Extra-gastrointestinal stromal tumor of the pancreas: A case report

Introduction

Presentation of case

Clinical discussion

Conclusion

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Pancreatic EGIST is extremely rare.

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There are no specific clinical and radiologic findings.

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Surgical resection is the cornerstone of the treatment.

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Whenever possible, enucleation is sufficient.

Cost-Effectiveness Analysis of Tyrosine Kinase Inhibitors in Gastrointestinal Stromal Tumor: A Systematic Review

Background: The introduction of tyrosine kinase inhibitor (TKI) therapy has dramatically improved the clinical effectiveness of patients with locally advanced and/or metastatic gastrointestinal stromal tumors (GIST), and this systematic review was conducted aiming at the cost-effectiveness analysis of TKIs in GIST.

Methods: A thorough literature search of online databases was performed, using appropriate terms such as “gastrointestinal stromal tumor or GIST,” “cost-effectiveness,” and “economic evaluation.” Data extraction was conducted independently by two authors, and completeness of reporting and quality of the evaluation were assessed. The systematic review was conducted following the PRISMA statement.

Results: Published between 2005 and 2020, 15 articles were incorporated into the systematic review. For advanced GIST, imatinib followed by sunitinib was considered cost-effective, and regorafenib was cost-effective compared with imatinib re-challenge therapy in the third-line treatment. For resectable GIST, 3-year adjuvant imatinib therapy represented a cost-effective treatment option. The precision medicine-assisted imatinib treatment was cost-effective compared with empirical treatment.

Conclusion: Although identified studies varied in predicted costs and quality-adjusted life years, there was general agreement in study conclusions. More cost-effectiveness analysis should be conducted regarding more TKIs that have been approved for the treatment of GIST.

Systematic Review Registration:https://www.crd.york.ac.uk/, PROSPERO: CRD42021225253.

Resection of a large gastrointestinal stromal tumor in the stomach after imatinib treatment in a 90-year-old patient

A 90-year-old woman presented with a 1-month history of progressive abdominal fullness. Contrast computed tomography (CT) showed a large 17-cm mass located adjacent to the antrum of the stomach without metastatic lesions. She underwent endoscopic ultrasound-guided fine-needle aspiration for diagnosis. Aspiration specimens revealed spindle-shaped cells positive for KIT by immunohistochemistry, with exon 11 mutations of the c-kit gene according to a genetic test. We ultimately diagnosed her with gastrointestinal stromal tumor (GIST). We judged the feasibility of imatinib treatment based on physiological and comprehensive geriatric assessments. We administered imatinib to reduce the tumor size and expected an excellent response based on genetic testing. After 5 months of imatinib administration with therapeutic drug monitoring (TDM), the tumor shrank by 42%. Six months later, there was no significant uptake of 18F-fluorodeoxyglucose on positron emission tomography. We successfully performed partial gastrectomy as conversion surgery, and she was carefully observed without any medication for 10 months after surgery. Here, we report a super elderly patient aged 90 years with a large GIST harboring an exon 11 mutation who underwent surgery after imatinib treatment with appropriate dose reduction during TDM after comprehensive geriatric assessment.

Cost-effectiveness Analysis of Genetic Testing and Tailored First-Line Therapy for Patients With Metastatic Gastrointestinal Stromal Tumors

IMPORTANCE

Gastrointestinal stromal tumor (GIST) is frequently driven by oncogenic KIT variations. Imatinib targeting of KIT marked a new era in GIST treatment and ushered in precision oncological treatment for all solid malignant neoplasms. However, studies on the molecular biological traits of GIST have found that tumors respond differentially to imatinib dosage based on the KIT exon with variation. Despite this knowledge, few patients undergo genetic testing at diagnosis, and empirical imatinib therapy remains routine. Barriers to genetic profiling include concerns about the cost and utility of testing.

OBJECTIVE

To determine whether targeted gene testing (TGT) is a cost-effective diagnostic for patients with metastatic GIST from the US payer perspective.

DESIGN, SETTING, AND PARTICIPANTS

This economic evaluation developed a Markov model to compare the cost-effectiveness of TGT and tailored first-line therapy compared with empirical imatinib therapy among patients with a new diagnosis of metastatic GIST. The main health outcome, quality-adjusted life years (QALYs), and costs were obtained from the literature, and transitional probabilities were modeled from disease progression and survival estimates from randomized clinical trials of patients with metastatic GIST. Data analyses were conducted October 2019 to January 2020.

EXPOSURE

TGT and tailored first-line therapy.

MAIN OUTCOMES AND MEASURES

The primary outcome was QALYs and cost. Cost-effectiveness was defined using an incremental cost-effectiveness ratio, with an incremental cost-effectiveness ratio less than $100 000/QALY considered cost-effective. One-way and probabilistic sensitivity analyses were conducted to assess model stability.

RESULTS

Therapy directed by TGT was associated with an increase of 0.10 QALYs at a cost of $9513 compared with the empirical imatinib approach, leading to an incremental cost-effectiveness ratio of $92 100. These findings were sensitive to the costs of TGT, drugs, and health utility model inputs. Therapy directed by TGT remained cost-effective for genetic testing costs up to $3730. Probabilistic sensitivity analysis found that TGT-directed therapy was considered cost-effective 70% of the time.

CONCLUSIONS AND RELEVANCE

These findings suggest that using genetic testing to match treatment of KIT variations to imatinib dosing is a cost-effective approach compared with empirical imatinib.

Treatment of gastrointestinal tumor (GIST) of the rectum requiring abdominoperineal resection following neoadjuvant imatinib: a cost-effectiveness analysis

Background

Neoadjuvant imatinib for gastrointestinal stromal tumors (GIST) of the rectum can reduce, but may not eliminate, risk of surgical morbidity from permanent bowel diversion. We sought to evaluate the cost-effectiveness of alternative strategies in rectal GIST patients requiring abdominoperineal resection following neoadjuvant imatinib.

Methods

We developed a Markov model using a healthcare payers' perspective to estimate costs in 2017 Singapore dollars (SGD) and quality adjusted life years (QALYs) for upfront abdominoperineal resection (UAPR) versus continued imatinib until progression (CIUP) following 1 year of neoadjuvant imatinib. Transition probabilities and utilities were obtained from published data, and costs were estimated using data from the National Cancer Centre Singapore. Deterministic and probabilistic sensitivity analyses were conducted to probe model uncertainty. Incremental cost-effectiveness ratio below SGD 50,000 per QALY gained was considered cost-effective.

Results

In the base case, UAPR dominates CIUP being both more effective (8.66 QALYS vs 5.43 QALYs) and less expensive (SGD 312,627 vs SGD 339,011). These estimates were most sensitive to 2 variables, utility of abdominoperineal resection and annual recurrence probability post-abdominoperineal resection. However, simultaneously varying the values of these variables to maximally favor CIUP did not render it the more cost effective strategy at willingness to pay (WTP) of SGD 50,000. In probabilistic sensitivity analysis, UAPR had probability of being cost-effective compared with CIUP greater than 95%, reaching 100% at WTP SGD 10,000.

Conclusion

UAPR is more effective and less costly than CIUP for patients with rectal GIST requiring abdominoperineal resection following neoadjuvant imatinib, and is the strategy of choice in this setting.

Optimizing the dose in patients treated with imatinib as first line treatment for gastrointestinal stromal tumours: A cost-effectiveness study

Aims

Patients with metastatic gastrointestinal stromal tumours (GIST) are treated in first line with the oral tyrosine kinase inhibitor, imatinib, until progressive disease. With this fixed dosing regimen, only approximately 40% of patients reach adequate plasma levels within the therapeutic index. Therapeutic drug monitoring (TDM) is a solution to reach plasma levels within the therapeutic index. However, introducing TDM will also increase costs, due to prolonged imatinib use and laboratory costs. The aim of this study was to evaluate the cost‐effectiveness of TDM in patients with metastatic/unresectable GIST treated with imatinib as a first line treatment, compared with fixed dosing.

Methods

A survival model was created to simulate progression, mortality and treatment costs over a 5‐year time horizon, comparing fixed dosing vs TDM‐guided dosing. The outcomes measured were treatments costs, life‐years and quality‐adjusted life‐years.

Results

Total costs over the 5‐year time horizon were estimated to be €106 994.85 and €150 477.08 for fixed dosing vs TDM‐guided dosing, respectively. A quality‐adjusted life year gain of 0.74 (95% confidence interval 0.66–0.90) was estimated with TDM‐guided dosing compared to fixed dosing. An average incremental cost‐effectiveness ratio of €58 785.70 per quality‐adjusted life year gained was found, mainly caused by longer use and higher dosages of imatinib.

Conclusion

Based on the currently available data, this analysis suggests that TDM‐guided dosing may be a cost‐effective intervention for patients with metastatic/unresectable GIST treated with imatinib which will be improved when imatinib losses its patency.

Evidence mapping based on systematic reviews of therapeutic interventions for gastrointestinal stromal tumors (GIST)

Background

Gastrointestinal Stromal Tumours (GISTs) are the most common mesenchymal tumours. Currently, different pharmacological and surgical options are used to treat localised and metastatic GISTs, although this research field is broad and the body of evidence is scattered and expanding. Our objectives are to identify, describe and organise the current available evidence for GIST through an evidence mapping approach.

Methods

We followed the methodology of Global Evidence Mapping (GEM). We searched Pubmed, EMBASE, The Cochrane Library and Epistemonikos in order to identify systematic reviews (SRs) with or without meta-analyses published between 1990 and March 2016. Two authors assessed eligibility and extracted data. Methodological quality of the included systematic reviews was assessed using AMSTAR. We organised the results according to identified PICO questions and presented the evidence map in tables and a bubble plot.

Results

A total of 17 SRs met eligibility criteria. These reviews included 66 individual studies, of which three quarters were either observational or uncontrolled clinical trials. Overall, the quality of the included SRs was moderate or high. In total, we extracted 14 PICO questions from them and the corresponding results mostly favoured the intervention arm.

Conclusions

The most common type of study used to evaluate therapeutic interventions in GIST sarcomas has been non-experimental studies. However, the majority of the interventions are reported as beneficial or probably beneficial by the respective authors of SRs. The evidence mapping is a useful and reliable methodology to identify and present the existing evidence about therapeutic interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12874-017-0402-9) contains supplementary material, which is available to authorized users.

How to Appropriately Extrapolate Costs and Utilities in Cost-Effectiveness Analysis

Costs and utilities are key inputs into any cost-effectiveness analysis. Their estimates are typically derived from individual patient-level data collected as part of clinical studies the follow-up duration of which is often too short to allow a robust quantification of the likely costs and benefits a technology will yield over the patient's entire lifetime. In the absence of long-term data, some form of temporal extrapolation-to project short-term evidence over a longer time horizon-is required. Temporal extrapolation inevitably involves assumptions regarding the behaviour of the quantities of interest beyond the time horizon supported by the clinical evidence. Unfortunately, the implications for decisions made on the basis of evidence derived following this practice and the degree of uncertainty surrounding the validity of any assumptions made are often not fully appreciated. The issue is compounded by the absence of methodological guidance concerning the extrapolation of non-time-to-event outcomes such as costs and utilities. This paper considers current approaches to predict long-term costs and utilities, highlights some of the challenges with the existing methods, and provides recommendations for future applications. It finds that, typically, economic evaluation models employ a simplistic approach to temporal extrapolation of costs and utilities. For instance, their parameters (e.g. mean) are typically assumed to be homogeneous with respect to both time and patients' characteristics. Furthermore, costs and utilities have often been modelled to follow the dynamics of the associated time-to-event outcomes. However, cost and utility estimates may be more nuanced, and it is important to ensure extrapolation is carried out appropriately for these parameters.

Cost-effectiveness of precision medicine in gastrointestinal stromal tumor and gastric adenocarcinoma

Over the past 20 years, with the incorporation of genetic sequencing and improved understanding regarding the mechanisms of cancer growth/metastasis, novel targets and their associated treatments have emerged in oncology and are now regularly incorporated into the clinical care of patients in the US. Novel, more tumor-specific, non-chemotherapy agents, including agents that are commonly used in the treatment of patients with gastric adenocarcinoma (GA) and gastrointestinal stromal tumor (GIST), fall under a broader treatment strategy, termed "precision medicine". While diagnostic testing and associated treatments in metastatic GA (mGA) are costly and may produce marginal benefit, those associated with GIST, despite being costly, produce significant improvements in patient outcomes. Despite the significant difference in impact, the agents associated with these cancers have similar acquisition costs. In this paper, we will review the current literature regarding cost and cost-effectiveness associated with precision medicine diagnosis and treatment strategies for GA and GIST.

Economic Evaluations of Pharmaceuticals Granted a Marketing Authorisation Without the Results of Randomised Trials: A Systematic Review and Taxonomy

BACKGROUND

Pharmaceuticals are usually granted a marketing authorisation on the basis of randomised controlled trials (RCTs). Occasionally the efficacy of a treatment is assessed without a randomised comparator group (either active or placebo).

OBJECTIVE

To identify and develop a taxonomic account of economic modelling approaches for pharmaceuticals licensed without RCT data.

METHODS

We searched PubMed, the websites of UK health technology assessment bodies and the International Society for Pharmacoeconomics and Outcomes Research Scientific Presentations Database for assessments of treatments granted a marketing authorisation by the US Food and Drug Administration or European Medicines Agency from January 1999 to May 2014 without RCT data (74 indications). The outcome of interest was the approach to modelling efficacy data.

RESULTS

Fifty-one unique models were identified in 29 peer-reviewed articles, 30 health technology appraisals, and 15 International Society for Pharmacoeconomics and Outcomes Research abstracts concerning 30 indications (44 indications had not been modelled). We noted the high rate of non-submission to health technology assessment agencies (28/98). The majority of models (43/51) were based on 'historical controls'-comparisons to previous meta-analysis or pooling of trials (5), individual trials (16), registries/case series (15), or expert opinion (7). Other approaches used the patient as their own control, performed threshold analysis, assumed time on treatment was added to overall survival, or performed cost-minimisation analysis.

CONCLUSIONS

There is considerable variation in the quality and approach of models constructed for drugs granted a marketing authorisation without a RCT. The most common approach is of a naive comparison to historical data (using other trials/registry data as a control group), which has considerable scope for bias.

Extrapolating Survival from Randomized Trials Using External Data: A Review of Methods

This article describes methods used to estimate parameters governing long-term survival, or times to other events, for health economic models. Specifically, the focus is on methods that combine shorter-term individual-level survival data from randomized trials with longer-term external data, thus using the longer-term data to aid extrapolation of the short-term data. This requires assumptions about how trends in survival for each treatment arm will continue after the follow-up period of the trial. Furthermore, using external data requires assumptions about how survival differs between the populations represented by the trial and external data. Study reports from a national health technology assessment program in the United Kingdom were searched, and the findings were combined with “pearl-growing” searches of the academic literature. We categorized the methods that have been used according to the assumptions they made about how the hazards of death vary between the external and internal data and through time, and we discuss the appropriateness of the assumptions in different circumstances. Modeling choices, parameter estimation, and characterization of uncertainty are discussed, and some suggestions for future research priorities in this area are given.

Peritonectomy and hyperthermic intraperitoneal chemotherapy: cost analysis and sustainability

BACKGROUND

Malignancies of the peritoneum remain a challenge in any hospital that accepts to manage them, due not only to difficulties associated with the complexity of the procedures involved but also the costs, which - in Italy and other countries that use a diagnosis-related group (DRG) system - are not adequately reimbursed.

MATERIAL AND METHODS

We analyzed data relative to 24 patients operated on between September 2010 and May 2013 with special regard to operating room expenditure, ICU stay, duration of hospitalization, and DRG reimbursement. The total costs per patient included clinical, operating room, procedure, pathology, imaging, ward care, allied healthcare, pharmaceutical, and ICU costs.

RESULTS

Postoperative hospital stay, drugs and materials, and operating room occupancy were the main factors affecting the expenditure for cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. We had a median hospitalization of 14 days, median ICU stay of 2.4 days, and median operating room occupancy of 585 min. The median expenditure for each case was € 21,744; the median reimbursement by the national health system € 8,375.

CONCLUSIONS

In a DRG reimbursement system, the economic effort in the management of patients undergoing peritonectomy procedures may not be counterbalanced by adequate reimbursement. Joint efforts between medical and administration parties are mandatory to develop appropriate treatment protocols and keep down the costs.

Comparison of anticipated and actual control group outcomes in randomised trials in paediatric oncology provides evidence that historically controlled studies are biased in favour of the novel treatment

BACKGROUND

Historically controlled studies are commonly undertaken in paediatric oncology, despite their potential biases. Our aim was to compare the outcome of the control group in randomised controlled trials (RCTs) in paediatric oncology with those anticipated in the sample size calculations in the protocols. Our rationale was that, had these RCTs been performed as historical control studies instead, the available outcome data used to calculate the sample size in the RCT would have been used as the historical control outcome data.

METHODS

A systematic search was undertaken for published paediatric oncology RCTs using the Cochrane Central Register of Controlled Trials (CENTRAL) database from its inception up to July 2013. Data on sample size assumptions and observed outcomes (timetoevent and proportions) were extracted to calculate differences between randomised and historical control outcomes, and a one-sample t-test was employed to assess whether the difference between anticipated and observed control groups differed from zero.

RESULTS

Forty-eight randomised questions were included. The median year of publication was 2005, and the range was from 1976 to 2010. There were 31 superiority and 11 equivalence/noninferiority randomised questions with time-to-event outcomes. The median absolute difference between observed and anticipated control outcomes was 5.0% (range: -23 to +34), and the mean difference was 3.8% (95% CI: +0.57 to +7.0; P = 0.022).

CONCLUSIONS

Because the observed control group (that is, standard treatment arm) in RCTs performed better than anticipated, we found that historically controlled studies that used similar assumptions for the standard treatment were likely to overestimate the benefit of new treatments, potentially leading to children with cancer being given ineffective therapy that may have additional toxicity.

Prevalence of gastrointestinal stromal tumour (GIST) in the United Kingdom at different therapeutic lines: an epidemiologic model

BACKGROUND

The prevalence of patients with gastrointestinal stromal tumourgst (GIST) who fail currently available treatments imatinib and sunitinib (third-line treatment-eligible GIST) is unknown, but is expected to be below an ultra-orphan disease threshold of 2/100,000 population used in England and Wales. Our study was designed to estimate the prevalence and absolute number of UK patients with unresectable/metastatic GIST at first-, second- and eventually third-line treatment.

METHODS

Our open population model estimates the probability that the prevalence of UK third-line treatment-eligible GIST patients will remain under the ultra-orphan disease threshold. Model parameters for incidence, proportion of unresectable/metastatic disease and survival estimates for GIST patients were obtained from a targeted literature review and a UK cancer register. The robustness of the results was checked through differing scenarios taking extreme values of the input parameters.

RESULTS

The base-case scenario estimated a prevalence of third-line treatment-eligible GIST of 1/100,000 and a prevalence count of 598 with a 99.9% likelihood of being below the ultra-orphan disease threshold. The extreme scenarios, one-way and probabilistic sensitivity analyses and threshold analysis confirmed the robustness of these results.

CONCLUSIONS

The prevalence of third-line treatment-eligible GIST is very low and highly likely below the ultra-orphan disease threshold.

The timing and probability of treatment switch under cost uncertainty: an application to patients with gastrointestinal stromal tumor

BACKGROUND

Cost fluctuations render the outcome of any treatment switch uncertain, so that decision makers might have to wait for more information before optimally switching treatments, especially when the incremental cost per quality-adjusted life year (QALY) gained cannot be fully recovered later on.

OBJECTIVE

To analyze the timing of treatment switch under cost uncertainty.

METHODS

A dynamic stochastic model for the optimal timing of a treatment switch is developed and applied to a problem in medical decision taking, i.e. to patients with unresectable gastrointestinal stromal tumour (GIST).

RESULTS

The theoretical model suggests that cost uncertainty reduces expected net benefit. In addition, cost volatility discourages switching treatments. The stochastic model also illustrates that as technologies become less cost competitive, the cost uncertainty becomes more dominant. With limited substitutability, higher quality of technologies will increase the demand for those technologies disregarding the cost uncertainty. The results of the empirical application suggest that the first-line treatment may be the better choice when considering lifetime welfare.

CONCLUSIONS

Under uncertainty and irreversibility, low-risk patients must begin the second-line treatment as soon as possible, which is precisely when the second-line treatment is least valuable. As the costs of reversing current treatment impacts fall, it becomes more feasible to provide the option-preserving treatment to these low-risk individuals later on.

A systematic review of 131I-meta iodobenzylguanidine molecular radiotherapy for neuroblastoma

The optimal use and effectiveness of (131)I-meta iodobenzylguanidine ((131)I-mIBG) molecular radiotherapy for neuroblastoma remain unclear despite extensive clinical experience. This systematic review aimed to improve understanding of the current data and define uncertainties for future clinical trials. Bibliographic databases were searched for neuroblastoma and (131)I-mIBG. Clinical trials and non-comparative case series of (131)I-mIBG therapy for neuroblastoma were included. Two reviewers assessed papers for inclusion using the title and abstract with consensus achieved by discussion. Data were extracted by one reviewer and checked by a second. Studies with multiple publications were reported as a single study. The searches yielded 1216 citations, of which 51 publications reporting 30 studies met our inclusion criteria. No randomised controlled trials (RCTs) were identified. In two studies (131)I-mIBG had been used as induction therapy and in one study it had been used as consolidation therapy. Twenty-seven studies for relapsed and refractory disease were identified. Publication dates ranged from 1987 to 2012. Total number of patients was 1121 with study sizes ranging from 10 to 164. There was a large amount of heterogeneity between the studies with regard to patient population, treatment schedule and response assessment. Study quality was highly variable. The objective tumour response rate reported in 25 studies ranged from 0% to 75%, mean 32%. We conclude that (131)I-mIBG is an active treatment for neuroblastoma, but its place in the management of neuroblastoma remains unclear. Prospective randomised trials are essential to strengthen the evidence base.

The economic impact of cytoreductive surgery and tyrosine kinase inhibitor therapy in the treatment of advanced gastrointestinal stromal tumours: a Markov chain decision analysis

PURPOSE

The current first-line treatment for patients with recurrent or metastatic gastrointestinal stromal tumours (GIST) is management with tyrosine kinase inhibition (TKI). There is an undefined role for surgery in the management of these patients. This study uses a cost analysis to examine the economic impact of treating patients with TKI in combination with surgery at different time-points in their treatment trajectories.

METHODS

A Markov chain decision analysis was modelled over a 2-year time horizon to determine costs associated with surgery in combination with imatinib mesylate (IM) or sunitinib malate (SU) in seven scenarios varied by TKI agent, dose and disease status (stable versus localised progressive disease). Rates of disease progression, surgical morbidity, mortality and adverse drug reactions were extracted from the existing literature. Deterministic sensitivity analyses were performed to examine changes in cost due to variations in key variables.

RESULTS

The least-costly scenario was to perform no surgery. The most costly scenario was to perform surgery on patients with localised progressive disease on IM 800 mg. The overall range of costs clustered within approximately $47,000 (USD). Variations in surgical cost, surgical mortality and cost of IM demonstrated thresholds for changing the least-costly scenario within plausible tested ranges.

CONCLUSION

Costs of surgical intervention at different time-points within the treatment course of patients with advanced GIST fluctuate within a relatively narrow range, suggesting that costs arise primarily from the administration of TKI. The decision to pursue cytoreductive surgery should not be based on cost alone. Future studies should incorporate health-state utilities when available.

Imatinib as adjuvant therapy for gastrointestinal stromal tumors: a systematic review

The high risk of recurrence in resected gastrointestinal stromal tumor (GIST) highlights the need for effective adjuvant treatment. This review evaluates the clinical efficacy and safety of imatinib for adjuvant treatment of localized KIT (CD117)-positive resected GIST. Relevant studies were identified by searching several electronic databases from inception to August 2009. Searches were supplemented by examining bibliographies of included studies, searching conference proceedings and consulting experts. All study types were included. Methodological quality was assessed using published criteria. Sixteen studies met the eligibility criteria, comprising one randomized controlled trial (RCT), three phase II studies, three cohort studies and nine case reports. In the RCT, the estimated 1-year recurrence-free survival was 98% [95% confidence interval (CI), 96-100] in the imatinib group versus 83% (95% CI, 78-88) in the placebo group, corresponding to a 65% reduction in the risk of disease recurrence (hazard ratio, 0.35; 95% CI, 0.22-0.53; p < 0.0001) with an absolute recurrence-free survival difference of 15% at 1 year. Other nonrandomized studies reported similar outcomes demonstrating that imatinib used in the adjuvant setting improved recurrence-free survival. The optimum duration of adjuvant treatment, safety and efficacy is currently under investigation with two ongoing RCTs (EORTC 62024 and SSG XV111) and two nonrandomized studies (NCT00867113 and NCT00171977). This study adds to the evidence (based on one RCT and a number of observational studies) that GIST patients treated with adjuvant imatinib therapy show an improvement in recurrence-free survival compared to placebo or no treatment after resection of KIT-positive localized GIST with tolerable toxicity.

Characterizing structural uncertainty in decision analytic models: a review and application of methods

BACKGROUND

The characterization of uncertainty is critical in cost-effectiveness analysis, particularly when considering whether additional evidence is needed. In addition to parameter and methodological uncertainty, there are other sources of uncertainty which include simplifications and scientific judgments that have to be made when constructing and interpreting a model of any sort. These have been classified in a number of different ways but can be referred to collectively as structural uncertainties.

MATERIALS AND METHODS

Separate reviews were undertaken to identify what forms these other sources of uncertainty take and what other forms of potential methods to explicitly characterize these types of uncertainties in decision analytic models. These methods were demonstrated through application to four decision models each representing one of the four types of uncertainty.

RESULTS

These sources of uncertainty fall into four general themes: 1) inclusion of relevant comparators; 2) inclusion of relevant events; 3) alternative statistical estimation methods; and 4) clinical uncertainty.Two methods to explicitly characterize such uncertainties were identified: model selection and model averaging. In addition, an alternative approach, adding uncertain parameters to represent the source of uncertainty was also considered.The applications demonstrate that cost-effectiveness may be sensitive to these uncertainties and the methods used to characterize them. The value of research was particularly sensitive to these uncertainties and the methods used to characterize it. It is therefore important, for decision-making purposes, to incorporate such uncertainties into the modeling process.

CONCLUSION

Only parameterizing the uncertainty directly in the model can inform the decision to conduct further research to resolve this source of uncertainty.

Verification of imatinib cost-effectiveness in advanced gastrointestinal stromal tumor in British Columbia (VINCE-BC study)

Background. This cost-effectiveness analysis of imatinib in British Columbia Cancer Agency (BCCA) patients with advanced gastrointestinal stromal tumors (GIST) was performed to justify funding.

Patients and Methods. A pragmatic, retrospective review identified BCCA patients with advanced GIST who received imatinib or historical treatment during successive, pre-specified time periods. Primary outcome was the cost-effectiveness (CE) of imatinib based on median overall survival (MOS). Secondary outcomes were cost-effectiveness based on median progression-free survival (PFS) and comparison to literature efficacy. This study took the BCCA perspective. Sensitivity analyses varying effectiveness over the 95% confidence interval (CI), cost to its extremes, discounting level at 0, 3, and 5%, and substituting life expectancy for MOS were performed.

Results. Forty-six and 47 patients in the imatinib and historical groups respectively showed MOS with imatinib to be 66.7 months (95%CI 61.7— infinity) compared to 7.7 (95%CI 6.0—12.6) in the historical group. Median-PFS were 45.3 months (95%CI 24.4—infinity) and 5.6 (95%CI 3.5—8.5) respectively. Imatinib effectiveness was similar to literature reports. The annual incremental CE ratio for imatinib was $15,882 CDN per median life year gained and $23,603 CDN per median year of PFS.

Conclusions. Imatinib for advanced GIST seems cost-effective in BC. Results were robust across a range of sensitivity analyses. J Oncol Pharm Practice (2008) 14: 105—112.

A pharmaco-economic analysis of second-line treatment with imatinib or sunitinib in patients with advanced gastrointestinal stromal tumours

Second-line treatments recommended by the National Cancer Center Network to manage advanced-stage gastrointestinal stromal tumours (GIST) were evaluated to determine the cost and cost-effectiveness of each intervention in the Mexican insurance system, the Instituto Mexicano del Seguro Social (IMSS). Treatments examined over a 5-year temporal horizon to estimate long-term costs included 800 mg day⁻¹ of imatinib mesylate, 50 mg day⁻¹ of sunitinib malate (administered in a 4 week on/2 week rest schedule), and palliative care. The mean cost (MC), cost-effectiveness, and benefit of each intervention were compared to determine the best GIST treatment from the institutional perspective of the IMSS. As sunitinib was not reimbursed at the time of the study, a Markov model and sensitivity analysis were conducted to predict the MC and likelihood of reimbursement. Patients taking 800 mg day⁻¹ of imatinib had the highest MC (±s.d.) of treatment at $35 225.61 USD (±1253.65 USD); while sunitinib incurred a median MC of $17 805.87 USD (±694.83 USD); and palliative care had the least MC over treatment duration as the cost was $2071.86 USD (±472.88 USD). In comparison to palliative care, sunitinib is cost-effective for 38.9% of patients; however, sunitinib delivered the greatest survival benefit as 5.64 progression-free months (PFM) and 1.4 life-years gained (LYG) were obtained in the economic model. Conversely, patients on imatinib and palliative care saw a lower PFM of 5.28 months and 2.58 months and also fewer LYG (only 1.31 and 1.08 years, respectively). Therefore, economic modeling predicts that reimbursing sunitinib over high dose imatinib in the second-line GIST indication would deliver cost savings to the IMSS and greater survival benefits to patients.

Cost-effectiveness of intraperitoneal chemohyperthermia in the treatment of peritoneal carcinomatosis from colorectal cancer

OBJECTIVES

Our purpose was to assess the cost-effectiveness of intraperitoneal chemohyperthermia (IPCH) compared to palliative chemotherapy (STANDARD) against peritoneal carcinomatosis arising from colorectal cancer.

METHODS

We performed a retrospective study of 96 patients whose peritoneal carcinomatosis had been diagnosed between January 1998 and December 2003 and treated either with IPCH or with palliative chemotherapy in French comprehensive cancer centers. Patients were followed up over a 3-year period. Effectiveness was measured by restricted mean survival at 3 years. The Bang and Tsiatis method was used to handle cost-censored data. The confidence limits of the mean cost per patient in each group and the mean incremental cost per life-year saved were computed using 1000 bootstrapreplicates. We also computed an acceptability curve for the incremental cost-effectiveness ratio (ICER).

RESULTS

We found that IPCH improved survival and was more costly than STANDARD treatment. Over a 3-year observation period, IPCH yielded an average survival gain of 8.3 months at the additional cost of euro58,086 (95% confidence interval 35,893-112,839) per life-year saved.

CONCLUSION

The ICER of IPCH is acceptable given the severity and burden of peritoneal carcinomatosis for which there is no alternative curative treatment.

The challenge of conducting pharmacoeconomic evaluations in oncology using crossover trials: the example of sunitinib for gastrointestinal stromal tumour

This paper examines the challenge of conducting economic evaluations to support patient access to cancer therapies when the cost-effectiveness estimation is hampered by crossover trial design. To demonstrate these limitations, we present the submission to the Canadian Drug Review (CDR) of a cost-effectiveness evaluation of sunitinib versus best supportive care (BSC) for the treatment of gastrointestinal stromal tumour in patients intolerant or resistant to imatinib. The economic model generated an incremental cost-effectiveness ratio for sunitinib versus BSC of dollars 79,884/quality-adjusted life-year gained. Eight months after initial submission, CDR granted a final recommendation to fund sunitinib following the manufacturer's appeal against their first recommendation. Although cost-effectiveness is an important consideration in reimbursement decisions, there is a need for improved decision-making processes for cancer drugs, as well as a better understanding of the limitations of clinical trial design.

Assessment of gastrointestinal stromal tumors with computed tomography following treatment with imatinib mesylate

AIM: To evaluate and characterize the patterns of disease progression of metastatic or unresectable gastrointestinal stromal tumor (GIST) treated with imatinib mesylate, and to determine the prognostic significance associated with disease progression.

METHODS: Clinical data and computed tomography (CT) images were retrospectively reviewed in 17 GIST patients who were treated with imatinib mesylate from October 2002 to October 2006. Apart from using size measurement for evaluation of tumor response [Response Evaluation Criteria in Solid Tumors (RECIST) criteria], patterns of CT changes during treatment were evaluated and correlated with clinical data.

RESULTS: There were eight non-responders and nine responders. Five patterns of CT change during treatment were found: focal progression (FP), generalized progression (GP), generalized cystic change (GC), new cystic lesion (NC) and new solid lesion (NS). At the end of study, all non-responders showed GP, whereas responders showed cystic change (GC and NC) and response according to RECIST criteria. Overall survival was significantly better in patients with cystic change or response within the RECIST criteria compared with GP patients (P = 0.0271).

CONCLUSION: Various patterns of CT change in patients with GIST who responded to imatinib mesylate were demonstrated, and might determine the prognosis of the disease. A combination of RECIST criteria and pattern of CT change are proposed for response evaluation in GIST.

Contribution of CT to treatment planning in patients with GIST

PURPOSE

The aim of this study was to illustrate the morphological and structural computed tomography (CT) patterns of gastrointestinal stromal tumours (GIST) and to discuss the technique's role in identifying lesions at a higher risk for malignant potential, in treatment planning and in the follow-up of patients with GIST.

MATERIALS AND METHODS

We retrospectively reviewed the CT scans of 26 patients who underwent surgery for histologically confirmed GIST of the stomach (20 cases), the duodenum (1), the caecum (1), the small bowel (2), the descending colon (1) and the rectum (1). CT exams were performed with a single-slice scanner and a 5-mm collimation before and after the intravenous administration of contrast material.

RESULTS

CT allowed us to correctly define the site, size and structure of lesions in all cases and to identify signs of invasion of neighbouring structures in some cases. The lesions exhibited solid density on the unenhanced scan and poor enhancement after contrast-medium administration; lesion structure was homogeneous in ten cases and inhomogeneous in 16; in one case, histology revealed microcalcification that had not been detected by CT.

CONCLUSIONS

CT, with its panoramic capabilities and high contrast resolution, provides essential information for treatment planning and for the follow-up of GIST patients treated with surgery or chemotherapy.

Cost effectiveness of imatinib mesylate in the treatment of advanced gastrointestinal stromal tumours

BACKGROUND AND OBJECTIVE

Imatinib mesylate is the first effective therapy for advanced unresectable gastrointestinal stromal tumours (GIST). Adoption of this therapy in clinical practice is partly dependent on reimbursement by third-party payers in many countries. The objective of this study was to estimate the cost effectiveness of imatinib mesylate in the treatment of GIST.

METHODS

A cost-effectiveness model of GIST treatment was developed. Long- term survival and duration of imatinib mesylate benefit were projected by fitting curves to 52-month follow-up data from a phase II clinical trial of imatinib and projecting weekly probabilities of survival and continued treatment over 10 years. Weekly cost estimates in 2005 US dollars included cost of imatinib mesylate 400 mg/day ($US685), other medical services for imatinib mesylate-treated patients ($US359) and palliative care for patients in the end stage of GIST ($US2575). Utility associated with successful treatment was estimated at 0.935 and that of treatment failure and progressive disease at 0.875. Costs, life-years and quality- adjusted life-years (QALYs) were calculated over the 10-year time horizon and discounted to treatment initiation at an annual rate of 3%.

RESULTS

Imatinib mesylate therapy for unresectable GIST was projected to increase life expectancy to 5.8 years, an increase of 2.7 years over the control group. This translated into an increase of 1.9 QALYs at a marginal cost of $US74 369, yielding a cost-effectiveness ratio of $US38 723 per QALY. Cost effectiveness was not very sensitive to model parameters other than the cost of imatinib mesylate itself.

CONCLUSION

The cost effectiveness of imatinib mesylate in the treatment of GIST is within the commonly accepted range for life-saving interventions, based on US data.

Treatment interruptions and non-adherence with imatinib and associated healthcare costs: a retrospective analysis among managed care patients with chronic myelogenous leukaemia

OBJECTIVES

Identify treatment interruptions and non-adherence with imatinib; examine the clinical and patient characteristics related to treatment interruptions and non-adherence; and estimate the association between treatment interruptions and non-adherence with imatinib and healthcare costs for US managed care patients with chronic myeloid leukaemia (CML).

METHODS

This retrospective analysis utilised electronic healthcare claims data from a US managed care provider. Adult patients with CML (as determined by International Classification of Diseases, ninth revision, Clinical Modification [ICD-9-CM] diagnosis code) were identified who began treatment with imatinib from 1 June 2001 through 31 March 2004. Treatment interruptions (i.e. failure to refill imatinib within 30 days from the run-out date of the prior prescription) were identified during the 12-month follow-up period. Medication possession ratio (MPR), calculated as total days' supply of imatinib divided by 365, was also examined. Healthcare costs (i.e. paid amounts for all prescription medications and medical services received, including health plan and patient liability) were examined in three ways: (i) total healthcare costs; (ii) total healthcare costs exclusive of imatinib costs; and (iii) total medical costs. All costs were converted to US dollars (2004 values) using the medical component of the Consumer Price Index. MPR was modelled using ordinary least squares regression. Presence of treatment interruptions was modelled using logistic regression. The association between MPR and healthcare costs was estimated using a generalised linear model specified with a gamma error distribution and a log link. All models included adjustment for age, gender, number of concomitant medications, starting dose of imatinib and cancer complexity.

RESULTS

A total of 267 patients were identified. Average age was approximately 50 years, and 43% were women. Mean MPR was 77.7%, with 31% of patients having a treatment interruption. However, all of these patients resumed imatinib within the study period. In this population, MPR decreased as the number of concomitant medications increased (p = 0.002), and was lower among women (p = 0.003), patients with high cancer complexity (p = 0.003) and patients with a higher starting dose of imatinib (p = 0.04). Women were approximately twice as likely as men to have a treatment interruption (p = 0.009), as were patients with a high cancer complexity (p = 0.03). After adjusting for the aforementioned covariates, MPR was found to be inversely associated with healthcare costs excluding imatinib (p < 0.001) and medical costs (p < 0.001). A 10% point difference in MPR was associated with a 14% difference in healthcare costs excluding imatinib and a 15% difference in medical costs. For example, patients with an MPR of 75% incur an additional 4072 US dollars in medical costs annually compared with patients with an MPR of 85%.

CONCLUSIONS

Treatment interruptions and non-adherence with imatinib, both of which could lead to undesired clinical and economic outcomes, appear to be prevalent. Physicians and pharmacists should educate patients and closely monitor adherence to therapy, as improving adherence and limiting treatment interruptions may not only optimise clinical outcomes but also reduce the economic burden of CML.

Clinical outcome in gastrointestinal stromal tumor patients who interrupted imatinib after achieving stable disease or better response

BACKGROUND

Imatinib has been found to be effective in the treatment of patients with gastrointestinal stromal tumors (GIST). We sought to evaluate the clinical outcome of imatinib interruption in GIST patients who had achieved stable disease (SD) or showed better response to imatinib therapy.

METHODS

From July 2001 to December 2004, we prospectively collected clinical data from 62 consecutive patients with advanced GIST, of whom 58 (93.5%) achieved SD or better response to imatinib therapy and were included in this study. Imatinib therapy was interrupted in 14 of the 58 patients (interruption group, INT), after a median time of 11.9 months. Progression-free survival (PFS) after imatinib interruption was calculated and imatinib-refractory PFS and overall survival (OS) were compared between the INT group and the 44 patients who continued imatinib treatment (continuation group, CONT).

RESULTS

After a median follow-up of 17.9 months following imatinib interruption, nine patients (64%) had progressive disease (PD) with a median PFS from the date of imatinib interruption of 10.0 months. Median PFS dated from the time of imatinib initiation in the INT group was 21.8 months (95% CI, 17.3-26.3 months), but was not reached in the CONT group (P=0.029). Following imatinib reintroduction in the INT group, 88% of patients achieved disease control. There were no statistically significant differences in imatinib-refractory PFS (P=0.405) and OS (P=0.498) between the groups.

CONCLUSION

In GIST patients controlled with imatinib, treatment might be interrupted, at least temporarily, when clinically warranted.

Follow-up of gastro-intestinal stromal tumours (GIST) during treatment with imatinib mesylate by abdominal MRI

Typical MRI findings for gastro-intestinal stromal tumours (GIST) under treatment with imatinib were evaluated. MRI was performed in 45 patients (25 responders, 20 non-responders) with metastatic or locally advanced, unresectable GIST. Target lesions were selected and re-evaluated after 2, 4, and 6 months of therapy with imatinib. The target tumour response (TTR) was classified according to RECIST criteria. TTR, signal intensity in the centre and border of the lesion and the presence and the extension of a hypervascular rim were analysed. The mean diameter of the marker lesions decreased significantly (P<0.001) from 7.1+/-2.6 cm to 5.9+/-2.3 cm after 6 months. Accuracy of RECIST criteria was 51%, 69% and 73% on MRI 2, 4 and 6 months for response assessment. In addition, responders had higher signal-to-noise ratios on T2-w images after 2 months (P<0.05) and a decrease of vascularised areas in the lesion 4 and 6 months after treatment (each P<0.01), when compared with non-responders. Beyond the size measurement for response assessment, MRI provides additional information of tumour response using SI of T2-w images and quantification of vascularised areas of GIST manifestations.