A Systematic Review of Health Technology Assessments of Chimeric Antigen Receptor T-Cell Therapies in Young Compared With Older Patients

Mixture and Non-mixture Cure Models for Health Technology Assessment: What You Need to Know

There is increasing interest in the use of cure modelling to inform health technology assessment (HTA) due to the development of new treatments that appear to offer the potential for cure in some patients. However, cure models are often not included in evidence dossiers submitted to HTA agencies, and they are relatively rarely relied upon to inform decision-making. This is likely due to a lack of understanding of how cure models work, what they assume, and how reliable they are. In this tutorial we explain why and when cure models may be useful for HTA, describe the key characteristics of mixture and non-mixture cure models, and demonstrate their use in a range of scenarios, providing Stata code. We highlight key issues that must be taken into account by analysts when fitting these models and by reviewers and decision-makers when interpreting their predictions. In particular, we note that flexible parametric non-mixture cure models have not been used in HTA, but they offer advantages that make them well suited to an HTA context when a cure assumption is valid but follow-up is limited.

Different Models, Same Results: Considerations When Choosing Between Approaches to Model Cost Effectiveness of Chimeric-Antigen Receptor T-Cell Therapy Versus Standard of Care

OBJECTIVE

Chimeric antigen-receptor T-cell therapy (CAR-T) is characterised by early phase data at the time of registration, high upfront cost and a complex manufacturing and administration process compared with standard therapies. Our objective was to compare the performance of different models to assess the cost effectiveness of CAR-T using a state-transition model (STM), partitioned survival model (PSM) and discrete event simulation (DES).

METHODS

Individual data for tisagenlecleucel for the treatment of young patients with acute lymphoblastic leukaemia (ALL) were used to populate the models. Costs and benefits were measured over a lifetime to generate a cost per quality-adjusted life-year (QALY). Model performance was compared quantitatively on the outcomes generated and a checklist developed summarising the components captured by each model type relevant to assessing cost effectiveness of CAR-T.

RESULTS

Models generated similar results with base-case analyses ranging from an incremental cost per QALY of $96,074-$99,625. DES was the only model to specifically capture CAR-T wait time, demonstrating a substantial loss of benefit of CAR-T with increased wait time.

CONCLUSION

Although model type did not meaningfully impact base-case results, the ability to incorporate an outcome-based payment arrangement (OBA) and wait time are important elements to consider when selecting a model for CAR-T. DES provided greater flexibility compared with STM and PSM approaches to deal with the complex manufacturing and administration process that can lead to extended wait times and substantially reduce the benefit of CAR-T. This is an important consideration when selecting a model type for CAR-T, so major drivers of uncertainty are considered in funding decisions.

Challenges and Lessons Learned in Autologous Chimeric Antigen Receptor T-Cell Therapy Development from a Statistical Perspective

Chimeric antigen receptor (CAR) T-cell therapy is a human gene therapy product where T cells from a patient are genetically modified to enable them to recognize desired target antigen(s) more effectively. In recent years, promising antitumor activity has been seen with autologous CAR T cells. Since 2017, six CAR T-cell therapies for the treatment of hematological malignancies have been approved by the Food and Drug Administration (FDA). Despite the rapid progress of CAR T-cell therapies, considerable statistical challenges still exist for this category of products across all phases of clinical development that need to be addressed. These include (but not limited to) dose finding strategy, implementation of the estimand framework, use of real-world data in contextualizing single-arm CAR T trials, analysis of safety data and long-term follow-up studies. This paper is the first step in summarizing and addressing these statistical hurdles based on the development of the six approved CAR T-cell products.

Economic Evaluations of Chimeric Antigen Receptor T-Cell Therapies for Hematologic and Solid Malignancies: A Systematic Review

OBJECTIVES

This study aimed to systematically review evidence on the cost-effectiveness of chimeric antigen receptor T-cell (CAR-T) therapies for patients with cancer.

METHODS

Electronic databases were searched in October 2022 and updated in September 2023. Systematic reviews, health technology assessments, and economic evaluations that compared costs and effects of CAR-T therapy in patients with cancer were included. Two reviewers independently screened studies, extracted data, synthesized results, and critically appraised studies using the Philips checklist. Cost data were presented in 2022 US dollars.

RESULTS

Our search yielded 1809 records, 47 of which were included. Most of included studies were cost-utility analysis, published between 2018 and 2023, and conducted in the United States. Tisagenlecleucel, axicabtagene ciloleucel, idecabtagene vicleucel, ciltacabtagene autoleucel, lisocabtagene maraleucel, brexucabtagene autoleucel, and relmacabtagene autoleucel were compared with various standard of care chemotherapies. The incremental cost-effectiveness ratio (ICER) for CAR-T therapies ranged from $9424 to $4 124 105 per quality-adjusted life-year (QALY) in adults and from $20 784 to $243 177 per QALY in pediatric patients. Incremental cost-effectiveness ratios were found to improve over longer time horizons or when an earlier cure point was assumed. Most studies failed to meet the Philips checklist due to a lack of head-to-head comparisons and uncertainty surrounding CAR-T costs and curative effects.

CONCLUSIONS

CAR-T therapies were more expensive and generated more QALYs than comparators, but their cost-effectiveness was uncertain and dependent on patient population, cancer type, and model assumptions. This highlights the need for more nuanced economic evaluations and continued research to better understand the value of CAR-T therapies in diverse patient populations.

Discrete Event Simulation to Incorporate Infusion Wait-Time When Assessing Cost-Effectiveness of a Chimeric-Antigen Receptor T Cell Therapy

OBJECTIVES

The main objective was to use discrete event simulation to model the impact of wait-time, defined as the time between leukapheresis and chimeric antigen receptor (CAR-T) infusion, when assessing the cost-effectiveness of tisagenlecleucel in young patients with relapsed/refractory acute lymphoblastic leukemia.

METHODS

The movement of patients through the model was determined by parametric time-to-event distributions, with the competing risk of an event determining the costs and quality-adjusted life-years (QALYs) assigned. Cost-effectiveness was expressed using the incremental cost-effectiveness ratio (ICER) for tisagenlecleucel compared with chemotherapy over the lifetime.

RESULTS

The base case generated a total of 5.79 QALYs and $622 872 for tisagenlecleucel and 1.19 QALYs and $181 219 for blinatumomab, resulting in an ICER of $96 074 per QALY. An increase in mean CAR-T wait-time to 6.20 months reduced the benefit and costs of tisagenlecleucel to 2.78 QALYs and $294 478 because of fewer patients proceeding to infusion, reducing the ICER to $71 112 per QALY. Alternatively, when the cost of tisagenlecleucel was assigned pre-infusion in sensitivity analysis, the ICER increased with increasing wait-time.

CONCLUSIONS

Under a payment arrangement where CAR-T cost is incurred post-infusion, the loss of benefit to patients is not reflected in the ICER. This may be misguiding to decision makers, where cost-effectiveness ratios are used to guide resource allocation. discrete event simulation is an important tool for economic modeling of CAR-T as it is amenable to capturing the impact of wait-time, facilitating better understanding of factors affecting service delivery and consequently informed decision making to deliver faster access to CAR-T for patients.

Cost-Effectiveness of Anti-BCMA Chimeric Antigen Receptor T Cell Therapy in Relapsed/Refractory Multiple Myeloma

Despite its promising outcomes, anti-BCMA chimeric antigen receptor T cell therapy (CAR-T) is the most expensive myeloma treatment developed to date, and its cost-effectiveness is an important issue. This study aimed to assess the cost-effectiveness of anti-BCMA CAR-T compared to standard antimyeloma therapy in patients with relapsed/refractory multiple myeloma. The model included myeloma patients in Japan and the United States who have received ≥3 prior lines of antimyeloma therapy, including immunomodulatory drugs, proteasome inhibitors, and anti-CD38 monoclonal antibodies. A Markov model was constructed to compare the CAR-T strategy, in which patients receive either idecabtagene vicleucel (ide-cel) or ciltacabtagene autoleucel (cilta-cel) followed by 3 lines of multiagent chemotherapy after relapse, and the no CAR-T strategy, in which patients receive only chemotherapy. Data from the LocoMMotion, KarMMa, and CARTITUDE-1 trials were extracted. Several assumptions were made regarding long-term progression-free survival (PFS) with CAR-T. Extensive scenario analyses were made regarding regimens for no CAR-T strategies. The outcome was an incremental cost-effectiveness ratio (ICER) with willingness-to-pay thresholds of ¥7,500,000 in Japan and $150,000 in the United States. When a 5-year PFS of 40% with cilta-cel was assumed, the ICER of the CAR-T strategy versus the no CAR-T strategy was ¥7,603,823 per QALY in Japan and $112,191 per QALY in the United States over a 10-year time horizon. When a 5-year PFS of 15% with ide-cel was assumed, the ICER was ¥20,388,711 per QALY in Japan and $261,678 per QALY in the United States over a 10-year time horizon. The results were highly dependent on the PFS assumption with CAR-T and were robust to changes in most other parameters and scenarios. Although anti-BCMA CAR-T can be cost-effective even under current pricing, a high long-term PFS is necessary.

High Cost of Chimeric Antigen Receptor T-Cells: Challenges and Solutions

Chimeric antigen receptor (CAR) T-cells are a cellular immunotherapy with remarkable efficacy in treating multiple hematologic malignancies but they are associated with extremely high prices that are, for many countries, prohibitively expensive. As their use increases both for hematologic malignancies and other indications, and large numbers of new cellular therapies are developed, novel approaches will be needed both to reduce the cost of therapy, and to pay for them. We review the many factors that lead to the high cost of CAR T-cells and offer proposals for reform.

How are health technology assessment bodies responding to the assessment challenges posed by cell and gene therapy?

BACKGROUND

The aims of this research were to provide a better understanding of the specific evidence needs for assessment of clinical and cost-effectiveness of cell and gene therapies, and to explore the extent that the relevant categories of evidence are considered in health technology assessment (HTA) processes.

METHODS

A targeted literature review was conducted to identify the specific categories of evidence relevant to the assessment of these therapies. Forty-six HTA reports for 9 products in 10 cell and gene therapy indications across 8 jurisdictions were analysed to determine the extent to which various items of evidence were considered.

RESULTS

The items to which the HTA bodies reacted positively were: treatment was for a rare disease or serious condition, lack of alternative therapies, evidence indicating substantial health gains, and when alternative payment models could be agreed. The items to which they reacted negatively were: use of unvalidated surrogate endpoints, single arm trials without an adequately matched alternative therapy, inadequate reporting of adverse consequences and risks, short length of follow-up in clinical trials, extrapolating to long-term outcomes, and uncertainty around the economic estimates.

CONCLUSIONS

The consideration by HTA bodies of evidence relating to the particular features of cell and gene therapies is variable. Several suggestions are made for addressing the assessment challenges posed by these therapies. Jurisdictions conducting HTAs of these therapies can consider whether these suggestions could be incorporated within their existing approach through strengthening deliberative decision-making or performing additional analyses.

Cost-effectiveness Analysis of Tisagenlecleucel Versus Blinatumomab in Children and Young Adults with Acute Lymphoblastic Leukemia: Partitioned Survival Model to Assess the Impact of an Outcome-Based Payment Arrangement

OBJECTIVE

This research assesses the impact of an outcome-based payment arrangement (OBA) linking complete remission (CR) to survival as a means of maintaining cost-effectiveness for a chimeric antigen receptor T cell (CAR-T) therapy in young patients with acute lymphoblastic leukemia (ALL).

METHODS

A partitioned survival model (PSM) was used to model the cost-effectiveness of tisagenlecleucel versus blinatumomab in ALL from the Australian healthcare system perspective. A decision tree modeled different OBAs by funneling patients into a series of PSMs based on response. Outcomes were informed by individual patient data, while costs followed Australian treatment practices. Costs and quality-adjusted life years (QALYs) were combined to calculate a single incremental cost-effectiveness ratio (ICER), reported in US dollars (2022) at a discount rate of 5% on costs and outcomes.

RESULTS

For the base case, incremental costs and benefit were $379,595 and 4.27 QALYs, giving an ICER of $88,979. The ICER was most sensitive to discount rate ($57,660-$75,081), "cure point" ($62,718-$116,206) and extrapolation method ($76,018-$94,049). OBAs had a modest effect on the ICER when response rates varied. A responder-only payment was the most effective arrangement for maintaining the ICER ($88,249-$89,434), although this option was associated with the greatest financial uncertainty. A split payment arrangement (payment on infusion followed by payment on response) reduced variability in the ICER ($82,650-$99,154) compared with a single, upfront payment ($77,599-$107,273).

CONCLUSION

OBAs had a modest impact on reducing cost-effectiveness uncertainty. The value of OBAs should be weighed against the additional resources needed to administer such arrangements, and importantly overall cost to government.

Systematic review of costs and cost-effectiveness of treatment for relapsed/refractory acute leukaemia in children and young adults

INTRODUCTION

Survival outcomes of children with relapsed/refractory (r/r) acute leukaemia remain poor. Novel expensive treatments have been developed to improve their outcomes, yet, limited evidence exists about cost-effectiveness of alternative treatment strategies.

AREAS COVERED

A systematic review was conducted to summarize the health-economic evidence about costs/cost-effectiveness of treating r/r acute leukaemia in children/young adults. We searched Medline, Embase, and Cochrane databases until August 13^th, 2021. Eligible articles included peer-reviewed original studies addressing r/r paediatric/young-adult acute lymphoblastic leukaemia (ALL), and acute myeloid leukaemia (AML). Quality assessment was conducted using Consolidated Health Economics Evaluation Reporting Standards (CHEERS) checklist.

EXPERT OPINION

The majority of papers focused on CAR-T cell therapy, which is still a novel treatment for r/r ALL, and was found to be cost-effective, yet, there remain concerns over its long-term effectiveness, affordability, and equity in access. The next best treatment option is Blinatumomab, followed by Clofarabine therapy, whereas FLA-IDA salvage chemotherapy provides least value for money. The quality of evidence is moderate to high, with limited generalizability of findings due to high variability in outcomes obtained from modelling studies. Limited studies evaluated r/r AML. We provide recommendations to deliver cost-effective treatments in real-world contexts, with implications for healthcare policy and practice.