OBJECTIVES: Less than 1/3 of Pharmaceutical Benefits Advisory Committee reimbursement submissions including a cost-effectiveness analysis (CEA - 2015-2020) were recommended; rare diseases carry a higher rate of approval at 50% (CEA - 2006-2020). Here we discuss some of the challenges and success factors in the reimbursement of siltuximab for idiopathic multicentric Castleman’s Disease (iMCD), a rare disease, on the Pharmaceutical Benefits Scheme.

METHODS: Reimbursement considerations included siltuximab’s position in the treatment algorithm, the appropriate comparator, use of available clinical trial data and modelling survival in a semi-Markov model framework. The challenges consisted of systematic elimination of unregistered comparators, conducting analyses from limited published survival data from clinical practice and the imputation of overall survival (OS) from 11 events in a small study population (N=79). The application of various scenarios assessing the long-term OS impact of model assumptions (including state-transition probabilities) were undertaken to optimise the results of the CEA. Expert Opinion was sought to achieve consensus to construct survival curves that mirror Australian current clinical practice. Unlike a partitioned survival model, this model allowed for some transition probabilities to vary over time particularly in treatment failure via tunnel substates. Lastly, we adjusted for cross-over and incorporated mature data. A 20-year horizon was taken, and a healthcare system perspective was adopted with both benefits and costs discounted at 5%.

RESULTS: An incremental cost effectiveness ratio of A$84,935 per Quality Adjusted Life Years (QALYs) was derived. At a willingness to pay threshold of $100,000/QALY, siltuximab has a 72.4% probability of being cost-effective compared with placebo (Best Supportive Care - BSC). Sensitivity analyses results were consistent with the base case.

CONCLUSIONS: As in other countries, higher Incremental Cost Effectiveness Ratio (ICER) thresholds for rare diseases are accepted. In the case of siltuximab in Australia, the value proposition was attractive and supported by funders, patients, and clinicians.