OP206 Expert Elicitation Of Probabilistic Distributions to Inform Survival Modelling of CD19 Chimeric Antigen Receptor T-Cell Therapies

Abstract

Introduction

In 2018, the National Centre for Pharmacoeconomics (NCPE) was commissioned to conduct a health technology assessment (HTA) of one of the first commercially available chimeric antigen receptor (CAR) T-cell therapies, tisagenlecleucel. CAR T-cells are a major advance in personalized cancer treatment, demonstrating promising outcomes in relapsed/refractory pediatric acute lymphoblastic leukemia (pALL). However, the results are based on short-term follow up, limiting their value in predicting long-term survival and leading to uncertainty about the most appropriate survival modeling method to employ. This study aimed to address these limitations by means of expert elicitation.

Methods

An expert elicitation method, the histogram technique, was employed. A predefined discrete numerical scale was presented in Microsoft Excel® and the expert was asked to place twenty crosses on a frequency chart. These crosses represented the expert's beliefs about the distribution of particular quantities. Each cross represented five percent of the probabilistic distribution. Individual distributions were then aggregated across experts using linear pooling.

Results

A total of seventeen experts were invited to take part; eight agreed to participate and five completed the exercise. Three experts did not consider tisagenlecleucel to be a “curative” therapy because patients had a higher risk of death, compared with the age- and sex-matched general population. The aggregated distributions indicated the five-year overall survival rate to be thirty-three percent (95% CI 8.65–56.88) in patients who do not receive a subsequent stem cell transplant and twenty percent (95% CI 2.38 -52.04) in those who do.

Conclusions

The results of this study will be used to calibrate CD19 CAR T-cell therapy survival estimates presented in HTA submissions to the NCPE to ensure more robust assessments. They will also be used to inform the construction of a de novo cost-utility model for examining the cost effectiveness of CD19 CAR T-cell therapies for relapsed/refractory pALL in the Irish healthcare setting.