Real world treatment patterns of gastrointestinal stromal tumor patients.

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Author(s): J. A. Morgan, A. Guo, D. Williams, A. Guérin, D. Latremouille-Viau, M. Tsaneva, A. P. Yu, E. Wu, J. Signorovitch, G. D. Demetri; Dana-Farber Cancer Institute, Boston, MA; Novartis Pharmaceuticals Corporation, East Hanover, NJ; Analysis Group, Inc., Boston, MA
Background: Imatinib is accepted as the standard first-line therapy to treat gastrointestinal stromal tumor (GIST) in patients with unresectable or metastatic disease. In the case of disease progression, physicians may consider increasing imatinib dose or switching to another second-line agent, such as sunitinib. The aim of this study was to analyze the real-world long term treatment patterns of GIST patients.
Methods: Two large claims databases from 01/1999 to 03/2008 were combined (MarketScan and Ingenix Impact) to extract patients diagnosed with GIST who initiated on imatinib ?400 mg/day. Patients were followed from the first observed imatinib prescription to the end of data availability. Patients who dose increased during the study period were defined as dose escalators, while patients who later switched to sunitinib with or without dose escalation were defined as switchers. Kaplan Meier analyses were used to estimate the rate of treatment changes over time including imatinib discontinuation, defined as a lack of imatinib supply for ?60 days, and switching back to initial treatment.
Results: Among the 1,508 GIST patients who initiated on imatinib, 253 patients had a dose increase and 153 patients switched to sunitinib during the study period. 20.1% patients on imatinib discontinued by the end of the first year, and 43.0% discontinued by the end of the third year. Among the 153 switchers, 61 patients had a dose escalation prior to the switch, of which 82.0% reached 800 mg before switching. Among all the switchers, 20.3% switched back to imatinib within 6 months.
Conclusions: These claims-based findings on the duration of first-line imatinib therapy of GIST patients supports data on imatinib efficacy in treating GIST from formal clinical research studies. Most of GIST patients who initiated imatinib continued on this therapy without undergoing dose increase or switch to sunitinib. Among switchers, most did not dose escalate before switching and many eventually switched back to imatinib. It appears that physicians tend to not always follow clinical practice guidelines developed based on expert consensus, with respect to decision rules for dose escalation, or for the appropriate time to change kinase inhibitor therapy.