Abstract
AIMS: Patients with metastatic gastrointestinal stromal tumours (GIST) are treated in first line with the oral tyrosine kinase inhibitor, imatinib, until progressive disease. With this fixed dosing regimen, only approximately 40% of patients reach adequate plasma levels within the therapeutic index. Therapeutic drug monitoring (TDM) is a solution to reach plasma levels within the therapeutic index. However, introducing TDM will also increase costs, due to prolonged imatinib use and laboratory costs. The aim of this study was to evaluate the cost-effectiveness of TDM in patients with metastatic/unresectable GIST treated with imatinib as a first line treatment, compared with fixed dosing. METHODS: A survival model was created to simulate progression, mortality and treatment costs over a 5-year time horizon, comparing fixed dosing vs TDM-guided dosing. The outcomes measured were treatments costs, life-years and quality-adjusted life-years. RESULTS: Total costs over the 5-year time horizon were estimated to be €106 994.85 and €150 477.08 for fixed dosing vs TDM-guided dosing, respectively. A quality-adjusted life year gain of 0.74 (95% confidence interval 0.66-0.90) was estimated with TDM-guided dosing compared to fixed dosing. An average incremental cost-effectiveness ratio of €58 785.70 per quality-adjusted life year gained was found, mainly caused by longer use and higher dosages of imatinib. CONCLUSION: Based on the currently available data, this analysis suggests that TDM-guided dosing may be a cost-effective intervention for patients with metastatic/unresectable GIST treated with imatinib which will be improved when imatinib losses its patency.