Adjuvant imatinib therapy of 208 gastrointestinal stromal tumor (GIST) patients: Dose, duration, and risk assessment.

Abstract

10061 Background: Imatinib (IM) is approved for adjuvant (ADJ) treatment (tx) of adult patients (pts) following complete, gross resection of GIST. In the IM registrational study, IM 400 mg was administered for one year. However, patient characteristics, tumor characteristics, dose, and duration of therapy are not known outside the context of a clinical trial. Methods: We used a data collection tool designed to provide insights into practice patterns surrounding the diagnosis and management of GIST pts (reGISTry) to explore nonclinical trial ADJ dosing in community and academic practices. Results: Since 11/04, 1,053 pts have entered the reGISTry. ADJ IM tx were reported as early as 2001 (n=1) with steady increases in 2007 (n=64) and 2008 (n=43). Most pts (56%) received ADJ therapy for over one year. Pts treated in the community seemed to receive a longer duration of therapy than those at academic centers (424d [2-1,970] vs. 348d [16-1,762]), but not statistically significant (p=0.21). Pts with small intestine primaries appeared to have a slightly longer duration of ADJ tx (433[3-1525] vs 378[2-1970] p=0.43), but no correlation with tumor size or mitotic count. Most pts (87%, 181/208) received IM 400 mg/d as the initial dose. 17.3% of ADJ IM dose changes were due to disease progression. Mitotic count was only reported in 33.6% of pts receiving ADJ tx. Conclusions: We found that most pts with primary GIST receive IM therapy at a dose of 400mg daily for more than one year. Duration of therapy did not appear to closely correlate with tumor size, site, or mitotic rate. Most pts receiving ADJ tx were treated without a known mitotic rate. Adjuvant imatinib in the tx of most pts with GIST does not appear to be based on standard, published, risk factors. Variable Adjuvant therapy N (%) Total = 208 No adjuvant therapy N (%) 1°localized GIST Tumor size >10 cm 73 (35.0) 162/658 (24.6) 2-5 cm 48 (23.0) 201/658 (30.5) Tumor location Stomach 109 (52.4) 397/660* (60.1) Small intestine 64 (30.8) 166/660* (25.1) Mitotic count >10/HPF 37 (17.8) 240/658 (11.9) 6-10/HPF 32 (15.4) 47/658 (7.1) * 2 pts did not have mitotic count or tumor size data available. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis Novartis Novartis Novartis