OBJECTIVES

: To estimate the budget impact, from the perspective of a one-million member US health plan, of using avapritinib to treat adult patients with unresectable or metastatic GIST with a PDGFRA exon 18 mutation, including a D842V mutation.

METHODS

: A budget impact model with a 3-year time horizon was developed in Microsoft Excel. The model included costs for drug acquisition, molecular testing, treatment monitoring, adverse events, and up to two subsequent lines of drug treatment following disease progression. The number of treated patients was based on age and gender-adjusted incidence of metastatic GIST, and a PDGFRA exon 18 mutation rate of 1.9%. Duration of treatment reflected median progression free survival from clinical trial data. The model assumed the introduction of avapritinib would increase PDGFRA molecular testing rates from the current rate of 49% to 69%. Base case assumptions also included a mixed 69% commercial, 22% Medicare, and 9% Medicaid population.

RESULTS

: Less than 0.1 new PDGFRA exon 18 patient per-year is estimated to be eligible for treatment. With avapritinib available, the average total incremental annual plan costs in years one, two, and three are $10,991, $27,992, and $46,994, respectively (per-member per-month $0.001, $0.002, and $0.004, respectively). These values include cost offsets of $577, $2,102, and $3,709 in avoided or delayed post-progression costs in years one, two, and three, respectively. In addition, the increased rates of molecular testing resulted in an incremental health plan testing cost of $453 in year three of avapritinib availability.

CONCLUSIONS

: The model results suggest that the use of avapritinib to treat patients with unresectable or metastatic GIST with a PDGFRA exon 18 mutation would result in a minimal budget impact to a US health plan, due to the small patient population and cost savings from reduced post-progression costs.