Correlation between imatinib trough levels and clinical benefit in gastrointestinal stromal tumors (GIST): Results of a prospective population pharmacokinetic study.

10014 Background: Imatinib is mainly metabolized in the liver. We therefore studied the potential effects of metastatic liver involvement on exposure to imatinib in patients with GIST. Additionally, as clearance from a retrospective analysis has been suggested to decrease over time (Judson et al., Cancer Chemother Pharmacol, 2005), while 1 month steady state imatinib trough levels were suggested to be associated with clinical benefit (Demetri et al., J Clin Oncol, 2009), the secondary endpoint of our study was to assess the exposure to imatinib after multiple long-term time-points. Methods: Multicenter prospective population pharmacokinetic study in 50 GIST patients treated with imatinib. Systemic exposure to imatinib was assessed through 24-hour pharmacokinetic sampling on day 1, month 1, 6 and 12. Patients were categorized in 4 groups based on their proportional metastatic liver volumes on CT images which were assessed on day 1, month 6 and 12 of therapy using OsiriX Imaging Software (OsiriX Foundation,...