E439: Cost-effectiveness of adjuvant imatinib in intermediate-risk gastrointestinal stromal tumors (GIST)

Adjuvant imatinib following resection of intermediate-risk gastrointestinal stromal tumors (GIST) is controversial, and current drug costs vary widely. We performed a cost-effectiveness analysis comparing three price points: industry pricing of generic imatinib, Medicare, and the Mark Cuban Cost Plus Drug Company (MCCPDC).

Methods:

We created a patient-level Markov microsimulation model including recurrence, next-line treatments, treatment complications, and overall survival based on published trial data. Costs of treatment and complications were included from a societal perspective over a ten-year time horizon, adjusted to 2022 US dollars, and extracted from published data, Medicare, and MCCPDC. Monthly imatinib (400mg) costs are $6,137.50 under industry pricing, $1,480.29 under Medicare, and $32.99 under MCCPDC. Utilities were determined based on previously published studies. The rate of recurrence for intermediate-risk GIST with no imatinib in the model was restricted to an annual recurrence rate between 15% and 50%. A willingness-to-pay (WTP) threshold of $100,000 per quality-adjusted life-years (QALYs) gained was used for all analyses.

Results:

Over a 10-year time horizon, the model predicted that initial treatment with imatinib was associated with negligible difference in QALYs compared to no imatinib amongst the three price points. When stratifying by the risk of recurrence, adjuvant imatinib was never cost-effective under industry pricing. Using Medicare pricing, adjuvant imatinib was cost-effective for patients with an annual recurrence risk above 45%. The current MCCPDC monthly imatinib price demonstrated cost-effectiveness at a recurrence risk of 35%. One-way sensitivity analyses were performed for all model parameters under Medicare pricing, showing that the model was most sensitive to the monthly cost of imatinib (Figure). For adjuvant imatinib therapy to be cost-effective at an annual risk of recurrence of 40%, the monthly Medicare cost for imatinib (400mg) must decrease by 81% from $1,480.29 to $268.77. No imatinib price demonstrated cost-effectiveness below a recurrence risk of 35%.

Conclusions:

Adjuvant imatinib therapy for resected GISTs is only cost-effective under MCCPDC prices for patients with a recurrence risk above 35%. With unclear benefits for overall survival, treatment decisions must consider recurrence risk and treatment toxicities such as cost.