Cost effectiveness of imatinib mesylate in the treatment of advanced gastrointestinal stromal tumours

Background and objective: Imatinib mesylate is the first effective therapy for advanced unresectable gastrointestinal stromal tumours (GIST). Adoption of this therapy in clinical practice is partly dependent on reimbursement by third-party payers in many countries. The objective of this study was to estimate the cost effectiveness of imatinib mesylate in the treatment of GIST. Methods: A cost-effectiveness model of GIST treatment was developed. Long-term survival and duration of imatinib mesylate benefit were projected by fitting curves to 52-month follow-up data from a phase II clinical trial of imatinib and projecting weekly probabilities of survival and continued treatment over 10 years. Weekly cost estimates in 2005 US dollars included cost of imatinib mesylate 400 mg/day ($US685), other medical services for imatinib mesylate-treated patients ($US359) and palliative care for patients in the end stage of GIST ($US2575). Utility associated with successful treatment was estimated at 0.935 and that of treatment failure and progressive disease at 0.875. Costs, life-years and quality-adjusted life-years (QALYs) were calculated over the 10-year time horizon and discounted to treatment initiation at an annual rate of 3%. Results: Imatinib mesylate therapy for unresectable GIST was projected to increase life expectancy to 5.8 years, an increase of 2.7 years over the control group. This translated into an increase of 1.9 QALYs at a marginal cost of $US74 369, yielding a cost-effectiveness ratio of $US38 723 per QALY. Cost effectiveness was not very sensitive to model parameters other than the cost of imatinib mesylate itself. Conclusion: The cost effectiveness of imatinib mesylate in the treatment of GIST is within the commonly accepted range for life-saving interventions, based on US data.